Really? OK lets Examine Beyond the Black River.
“Perhaps a panther—” began Balthus, without conviction.
Conan shook his head impatiently.
"A man from the Tauran couldn’t mistake the mark of a panther’s claws. No. It’s a forest devil summoned by Zogar Sag to carry out his revenge.
So right here you see that Zogar Sag is summoning things which he then SENDS OUT TO DO HIS BIDDING, not fighting out along side them nor turning into them. Also, Zogar Sag is a Priest of Jhebal Sag so this isn’t exactly a “Demon” mind you.
“Tiberias was an armed man,” grunted Conan. “If Zogar Sag can bring demons to aid him, he can tell them which men to kill and which to let alone. No, I didn’t see it. I only saw the bushes shake as it left the trail. But if you want further proof, look here!”
Again, Zogar Sag is controlling the “demons” he is summoning but not actively getting involved with the fighting nor turning into them.
He remembered what Valannus had said—that Zogar boasted that he could summon wild beasts to do his bidding.
A shuddering gasp swept over the village and men crowded hastily back, jamming one another between the huts. Balthus felt the short hair stir on his scalp. The creature that stood in the gate was like the embodiment of nightmare legend. Its color was of a curious pale quality which made it seem ghostly and unreal in the dim light. But there was nothing unreal about the low-hung savage head, and the great curved fangs that glistened in the firelight. On noiseless padded feet it approached like a phantom out of the past. It was a survival of an older, grimmer age, the ogre of many an ancient legend—a saber-tooth tiger.
Again Balthus recognized the monster from ancient legends. He saw and knew the ancient and evil serpent which swayed there, its wedge-shaped head, huge as that of a horse, as high as a tall man’s head, and its palely gleaming barrel rippling out behind it. A forked tongue darted in and out, and the firelight glittered on bared fangs.
Balthus became incapable of emotion. The horror of his fate paralyzed him. That was the reptile that the ancients called Ghost Snake, the pale, abominable terror that of old glided into huts by night to devour whole families. Like the python it crushed its victim, but unlike other constrictors its fangs bore venom that carried madness and death. It too had long been considered extinct. But Valannus had spoken truly. No white man knew what shapes haunted the great forests beyond Black River.
But this head was smaller, more narrow; it was a leopard which stood there, snarling silently and glaring down the trail. What wind there was was blowing toward the hiding men, concealing their scent. The beast lowered his head and snuffed the trail, then moved forward uncertainly. A chill played down Balthus’ spine. The brute was undoubtedly trailing them.
“He can’t command all the animals. Only such as remember Jhebbal Sag.”
So, from this very story you see that not only did Zogar Sag NOT ever once “turn into a demon”, he never even summoned any demons at all. He simply command animals, those who still remembered Jhebal Sag to carry out his bidding. So by your own “evidence” you are WRONG.
Now, if we look at -The Phoenix on The Sword- you will find this.
“Blind your eyes, mystic serpent,” he chanted in a blood-freezing whisper. “Blind your eyes to the moonlight and open them on darker gulfs! What do you see, oh serpent of Set? Whom do you call from the gulfs of the Night? Whose shadow falls on the waning Light? Call him to me, oh serpent of Set!”
Stroking the scales with a peculiar circular motion of his fingers, a motion which always carried the fingers back to their starting place, his voice sank still lower as he whispered dark names and grisly incantations forgotten the world over save in the grim hinterlands of dark Stygia, where monstrous shapes move in the dusk of the tombs.
There was a movement in the air about him, such a swirl as is made in water when some creature rises to the surface. A nameless, freezing wind blew on him briefly, as if from an opened Door. Thoth felt a presence at his back, but he did not look about. He kept his eyes fixed on the moonlit space of marble, on which a tenuous shadow hovered. As he continued his whispered incantations, this shadow grew in size and clarity, until it stood out distinct and horrific. Its outline was not unlike that of a gigantic baboon, but no such baboon ever walked the earth, not even in Stygia. Still Thoth did not look, but drawing from his girdle a sandal of his master—always carried in the dim hope that he might be able to put it to such use—he cast it behind him.
“Know it well, slave of the Ring!” he exclaimed. “Find him who wore it and destroy him! Look into his eyes and blast his soul, before you tear out his throat! Kill him! Aye,” in a blind burst of passion, “and all with him!”
Etched on the moonlit wall Thoth saw the horror lower its misshapen head and take the scent like some hideous hound. Then the grisly head was thrown back and the thing wheeled and was gone like a wind through the trees. The Stygian flung up his arms in maddened exultation, and his teeth and eyes gleamed in the moonlight.
And here you see Thoth Amon SUMMONING a demon to kill King Conan, and all of those who happen to be with him (the people who were actually attempting to kill him and who had enslaved Thoth-Amon after stealing his Serpent Ring of Set).
In -The God in The Bowl- one again Thoth-Amon sends something from who knows where or when out in a bowl to do his bidding in an attempt to slay Kalanthes a priest of the Iblis.
‘I found a symbol on the bottom of the Bowl!’ chattered Promero. ‘Not an ancient hieroglyphic, but a symbol recently carved! The mark of Thoth-amon, the Stygian sorcerer, Kalanthes’s deadly foe! He found it in some grisly cavern below the haunted pyramids! The gods of old times did not die, as men died—they fell into long sleeps and their worshippers locked them in sarcophagi so that no alien hand might break their slumbers. Thoth- amon sent death to Kalanthes—Kallian’s greed caused him to loose the horror—and it is lurking somewhere near us—even now it may be creeping upon us—’
'The men of the caravan did not know. They only said that the men who gave it to them told them that it was a priceless relic, found among the tombs far beneath the pyramids and sent to Kalanthes “because of the love the sender bore the priest of Ibis”. Kallian Publico believed that it contained the diadem of the giant-kings, of the people who dwelt in that dark land before the ancestors of the Stygians came there. He showed me a design carved on the lid, which he swore was the shape of the diadem which legend tells us the monster-kings wore.
Now, the story does not specifically state that Thoth-Amon summoned the entity in the bowl, but there are no other references to anything like it before or after so one can infer that he may very well have done so. At either rate, it is yet another example of an extremely powerful wizard sending forth a being to do their bidding for them and not actually going out and engaging in physical combat themself.
Now from -The Black Stranger- you have this.
‘I understand!’ he panted. 'He is playing with me, as a cat with a mouse. To have slain me last night in my chamber were too easy, too merciful. So he destroyed the ship in which I might have escaped him, and he slew that wretched Pict and left my chain upon him, so that the savages might believe I had slain him—they have seen that chain upon my neck many a time.
‘But why? What subtle deviltry has he in mind, what devious purpose no human mind can grasp or understand?’
‘Who is this black man?’ asked Belesa, chill fear crawling along her spine.
‘A demon loosed by my greed and lust to plague me throughout eternity!’ he whispered. He spread his long thin fingers on the table before him, and stared at her with hollow, weirdly luminous eyes that seemed to see her not at all, but to look through her and far beyond to some dim doom.
‘In my youth I had an enemy at court,’ he said, as if speaking more to himself than to her. 'A powerful man who stood between me and my ambition. In my lust for wealth and power I sought aid from the people of the black arts—a black magician, who, at my desire, raised up a fiend from the outer gulfs of existence and clothed it in the form of a man. It crushed and slew my enemy; I grew great and wealthy and none could stand before me. But I thought to cheat my fiend of the price a mortal must pay who calls the black folk to do his bidding.
'By his grim arts the magician tricked the soulless waif of darkness and bound him in hell where he howled in vain—I supposed for eternity. But because the sorcerer had given the fiend the form of a man, he could never break the link that bound it to the material world; never completely close the cosmic corridors by which it had gained access to this planet. A year ago in Kordava word came to me that the magician, now an ancient man, had been slain in his castle, with marks of demon fingers on his throat. Then I knew that the black one had escaped from the hell where the magician had bound him, and that he would seek vengeance upon me. One night I saw his demon face leering at me from the shadows in my castle hall—
'It was not his material body, but his spirit sent to plague me—his spirit which could not follow me over the windy waters. Before he could reach Kordava in the flesh, I sailed to put broad seas between me and him. He has his limitations. To follow me across the seas he must remain in his man-like body of flesh. But that flesh is not human flesh. He can be slain, I think, by fire, though the magician, having raised him up, was powerless to slay him—such are the limits set upon the powers of sorcerers.
‘But the black one is too crafty to be trapped or slain. When he hides himself no man can find him. He steals like a shadow through the night, making naught of bolts and bars. He blinds the eyes of guardsmen with sleep. He can raise storms and command the serpents of the deep, and the fiends of the night. I hoped to drown my trail in the blue rolling wastes—but he has tracked me down to claim his grim forfeit.’
So you see, the summoning of demons is.. not exactly safe. Things CAN go wrong. And when they do said demons CAN and WILL hunt you down and murder you.
The great hall was full of drifting wisps of smoke through which he groped, half-blinded. Somewhere a woman was whimpering, little, catchy, hysterical sobs of nerve-shattering horror. He emerged from a whorl of smoke and stopped dead in his tracks, glaring down the hall.
The hall was dim and shadowy with drifting smoke; the silver candelabrum was overturned, the candles extinguished; the only illumination was a lurid glow from the great fireplace and the wall in which it was set, where the flames licked from burning floor to smoking roof-beams. And limned against that lurid glare Conan saw a human form swinging slowly at the end of a rope. The dead face turned toward him as the body swung, and it was distorted beyond recognition. But Conan knew it was Count Valenso, hanged to his own roof-beam.
But there was something else in the hall. Conan saw it through the drifting smoke—a monstrous black figure, outlined against the hell-fire glare. That outline was vaguely human; but the shadow thrown on the burning wall was not human at all.
So by all means, you can continue to argue all you like, but I have sufficiently proven what I have said all along and have also proven your own example to be not only not what you claimed it to be but also to be in favor of what I have been saying (though with the use of summoning animals instead of demons).