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I don't think the rankings give that much XP though.

It gave none. A little COMP and a 1-tier item. Maybe I was wrong, but in the rewards list before the quest was over, it said experience. Or it gave it without mentioning it.

Faith might be your best choice

Nope. Not unless I buy lots of PART, and I don't want to do that. I want to grow organically.

finding a different guild

That could be an option, I guess.