I don't see what this has to do with what you're referring to. FATEs being a thing of the past will occur because everyone has leveled all their battle classes, which has nothing to do with how many options people have to level in groups.

Later dungeons could probably do with some extra experience points rewards, though, IMO. They could also make the Darkhold harder if they want to justify it someway, since that dungeon is currently disproportionately easy.