ok i've figured it out. there's actually a very clear and obvious "who has the right to mirrodin" argument beyond just "phyrexia ruthlessly destroyed the mirran's lives". are the new phyrexians basically native to argentum? sure... but! they're native to the core! they invaded the surface. the nps were born of the oil in the core and grew there. both nps and mirrans are native to mirrodin, they were born of an external stimulus that interacted with it. it's not really about who's originally from there, it's about the urge of one group to dominate the other
several characters end up talking about it in ways like this, where they're thinking about phyrexia as external. but i think that's a meaningless and frankly fraught trajectory to use when trying to figure out whose right is more just on topics of land and such. it's really a very simple situation that only gets twisted if you phrase your motivation strangely. it's not like phyrexians don't have a right to exist. but it's a false dichotomy to assume that there was only mirrodin or new phyrexia
that's part of why characters like urabrask are interesting. ultimately they may never have had a personality that could remain at peace with non-phyrexian societies. but the goal is "i just want to stay in my lane" is much more acceptable