It depends entirely on what method they use to transport people to it.
Exiles all start nailed to s cross in the Southern Dessert.

While not indicative of a land route, it heavily implies it, as do many of the letters and such found scattered about.

However, no one has been awake for the final hoisting or the final approach. So we don’t know.

Then we have the Siptah intro, that explicitly notes a ship of prisoners bound for the Exiled Lands being blown off course.
That explicitly notes a nautical route

Porque no los dos is a valid response.

However, that still doesn’t clarify how long the journey is, how far, and what supplies would be needed.
Whether Australia or Denmark, moving convicts to a place of banishment is easier than moving and maintaining supply lines for an Army.

If we can just march an army in and out, then an army can be marched in because there is a direct and reasonably traversable land route and the Exiled Lands are connected to the main continent.
Which is inconvenient for a fair amount of selective access pocket dimension established elsewhere.
Now, if at the ruins of Al Merayah, there were a big ole magic circle or teleport point, that would neatly explain everything.

Also, why Al Merayah (this one knows, it’s central ish on the map and not too close to any one Obelisk, but also not too far from any and the Dogs of the Dessert were already a bloated faction, not as bad as Black Hand, but still they have plenty of spots)? How is that the convenient staging location for an Army that marched in or was deposited by naval transport?
If it is hand in hand with Toth Amon, why not encamp in the ample no build plateau near Sepermeru, where there is an existing support network and closer to a potential border?
If it is in spite of Toth Amon or only barely approved, why not make landfall on the coast, or pick a spot with more fresh water that isn’t guarded by lions and elephants?

If it were building upon the actual ruins, that would be cool… But instead, it’s replacing them…
Why bother?

And in what cosmos are the small reserves of a pack of Exiles worth the attention of one of the more powerful, and most frequently embattled, armies of the era?

This one is reading too much into the matter, but the entire game has all these deliciously tantalizing breadcrumbs. Always enough to appetize, never enough to satisfy. Which is a compliment. But all these crumbs directly encourage over thinking.