It's a complicated situation, certainly, though Fourchenault is not really in a position to comment on it or decide the merit and weight of generational torment inflicted upon the very people who his deluded 'supreme deity' tormented the most as a consequence of the Sundering. I think it's telling that the game avoids bringing up that the Garleans and their difficulty manipulating aether is a direct consequence of Venat's 'grand plan'.

It's also possible for multiple groups of people to have a valid claim to a specific bit of land - though there's really no real reason that the game could not push for a compromise and have the Garlean survivors integrate into Corvos and return to their roots as farmers. The only reason it did not, I suspect, is because the game has ever been one sided in terms of how it goes about 'liberation' stories. An unfortunate consequence of the protagonist centred morality at play as well as the broken aesops. Incidentally, the Garleans are very similar to the Ancients in that regard. Both are races which were subjected to horrific atrocities, had to get their hands dirty in order to survive and then are blamed for not just rolling over and dying for the convenience of the self proclaimed 'heroes' of the story.