[Legate of Amon Lanc]

Apart from all other reasons, I would imagine there were at least some, one would say, purely "practical" and demographic reasons for why Éothéod was chosen and the Dunlendings were not.

The Éothéod were numerous people who were happy to leave their original land, we don't know as much about Dunlendings. Most of all, however, the Éothéod were obviously much more "nomadic" than Dunlendings. Do we know whether the Dunlendings would have actually wanted to leave their own country at that time? Sure, retrospectively they could have said whatever they wanted. But just think about it for a second. To approach a nation who is okay in the place where they are, they don't have any problems with being too many, sitting quite comfortably in their place, and ask them to move to the land you offer to them just because you ask them to, will majority of the nations actually respond positively to that? I think many would just shake their head at you, not being too happy with the prospect of starting completely anew as long as their original country is still okay to them.

Aside from everything else, even if we imagined that Gondor would have given Calenardhon to the Dunlendings, I am not really sure if it would have turned out to be a wise decision. The Dunlendings envied their neighbors, the Rohirrim, their land. What would they do if just around the corner there was a rich noble kingdom... I don't want to underestimate the Dunlendings, but with them in Calenardhon, I can easily imagine the Battle at the Pelennor Fields culminating with: "Horns! Horns!" - "Yea, guys, we heard that some Mordor decided to get rid of you, so we came to see if there isn't anything left to loot!"

So, maybe no, not really.