[Elmo]

The Dunlendings like any men weren't inherently evil. They in fact only turned over to the evil side because they were done out of the fertile lands of Calenardhon by the Rohirrim. If Calenardhon was so under-populated that Cirion could give the whole province up like he did to Eorl surely it would have been in Gondor's interest to give the land to a more nearby people than the far off Éothéod.

When offering the land they could have made the Dunlending swear an oath of eternal alliance etc. By giving them the land they would have gained the friendship of the Dunlendings and so gain a handy bulwark in their northern frontier. And maybe all the Balchoth mischief wouldn't have been so bad.