To be honest, I think that's something that the developers are working on. They've been working hard on balancing the whole game for YEARS now, and it seems like every new or returning player I've chatted with has had good things to say about their archetype, of they've chosen the right one. I don't see the developers slipping now.
There are several ways that they CAN alter Kheldian inherent abilities to accommodate "Leagues" as it is, either by dividing the standard bonus by a certain fraction, or by establishing that the first seven people in the league will set the bonuses. It might even be the case that Kheldians get to choose.
And if the Kheldian Inherent happens to accept bonuses from 47 people instead of 7 people, then I suppose we know that at least one character in the group will be able to finish things, if needed.
Too many alts to list.
From my understanding, it's individual teams linked together on one UI, meaning whatever your team of 8 has is what will benefit you, not the other teams.
Youmu has it right. Team only powers (e.g. leadership) will still only affect those in the team. We have no reason to believe Cosmic Balance will see anyone outside of the team.
Where to now?
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I read that teams for incarnate trials will be bigger. I wonder how this will interact with cosmic balance.