By power gamers, I mean people that bring top-tier competitive lists in a non-tournament setting. We generally gear leagues and campaigns as more of a "have fun" type deal, but obviously winning is part of it. The problem is there is a decent chunk of the community who bring their absolute best lists. This means that everyone else would have to do the same, and we all know there are certain squadron builds and even some entire ships you can't field in a competitive environment. So now the non-competitive players have to either field the ships they want to field and lose every game, or also bring a competitive list and not use a chunk of their collection. So I suppose not quite WAAC, but highly competitive players who bring their highly competitive lists into what are supposed to be more relaxed environments. So then our "just for fun" players stop coming, because they don't enjoy getting thrashed all the time and they want to bring the ships they want to bring. Even if your opponent is perfectly pleasant, a lot of people won't have fun losing multiple games a week for a month or more.
So, you're saying that your leagues are not there for people who play to win, but the people for whom those leagues are meant, will take their marbles home if they lose. That seems paradoxical.
But maybe I misunderstand what you mean by a league. I understand a league as essentially a longer-run tournament. That's at least how leagues are run in my area, and if you win more you get more swag from a tournament kit. That's not really a 'just-for-fun' set up the way that you're describing.
In terms of a campaign, I hear what you're saying. In a campaign the competitive spirit should give a bit of way to the common enjoyment of a narrative.
However, all of these events should focus on building community. It sounds like from the start your idea of leagues and campaigns is intended to exclude people with that competitive spirit, implying that their style of play is not appreciated. That doesn't build community.
I think that there should be room for catering to preferences, but if you're going to do that then you should make it explicit what itch you're trying to scratch with the activity. Don't bait and switch.