I’ve seen the Cimmerian Priest NPC, but it has been ultra rare and it’s a priest of Ymir, not Crom. Like others already mentioned, it’s not unreasonable to imagine that a few Cimmerians here and there might convert and worship one of the other gods. Most of the Cimmerians in the Mounds have the proper attitude towards Crom, e.g. “Crom’s poxy balls!”
Besides, the game allows you to create a Cimmerian player character and pick almost any in-game religion right at the start. And then you can run around the world and collect all the other religions. That’s so far from Howard’s source material, it might as well be in another galaxy – would you expect them to restrict that?
Here’s the thing: it’s a video game based on existing literature. Those are two different media and they have different requirements. The defining characteristic of video games, the one that sets them apart from other media, is the player agency. As Sid Meier famously put it, “a good game is a series of interesting choices”. That’s why usually everything in a good game is in service of gameplay, including the story, the world, the setting, the lore, etc.
What I’m getting at is that a certain degree “artistic license” if indispensable if you’re making a game.
So yes, you’re absolutely right about all those details. But I cannot agree with you that Funcom was taking the piss and “screwed with ALL of R. E. Howard’s lore.” That kind of hyperbole is not really reasonable.
Out of all your examples, I think the most egregious of Funcom’s lore screwups is the Poitainian katana. All the other examples are either reasonable artistic license or debatable 
for such a great analysis here in this thread!!