Mybb community, very immature.

[ZiNgA BuRgA]

I think making judgements on a single incident is a bit too hasty thinking.  I mean, there's a number of possible issues you may not be aware of, such as discussions in private (from my experience with the team, the ugliest stuff happens there).
I can't really say much about that person in question as I don't really know what's been going on there.

Unless you really hope to involve yourself with the community, I don't think you should abandon a software because you dislike the community.  I don't really like it, but I will still be using MyBB.  You can still easily gain support there without caring about sections such as Chit-Chat etc.  I mean, as long as you get what you want, it shouldn't really matter how mature the community is, right?  Of course, if you personally just prefer phpBB over MyBB, then by all means...

And I don't think it's unreasonable to show favouritism towards certain members.  If they're your biggest supporters, I think it's natural to really do so.  It can be considered an incentive to try to keep them supporting you in the future.  For example, if your employer is paying you well, it's only natural that you want to please him/her so that you keep your job there.
Now whether you think the level of favouritism is too much is another thing - with that, I'd probably agree there's probably a bit too much.