There has to be sufficient reason for the characters to be on screen, or it will just come off as contrived, and take us back to Yawnersville.
Since "in no way balanced" sounds pretty extreme, if not hyperbolic, I'd like a tally, please. There's some space in between "totally balanced" and "in no way balanced", namely "somewhat balanced".
I also think you're being disingenuous about mothers and girlfriends. They didn't "have" to be on screen at all! Strike any one of Winona, Amanda, Gaila, or even Hannity, and STXI is a noticeably lesser film, but it's still perfectly doable. (ETA:
Are women only legitimately on screen if they come stag and childless? I'm probably missing something here, but the main characters are already set in stone: Kirk and Spock and they're male. Is Carol not legitimately on screen because she's Admiral Marcus's daughter?)
Just how big does the set of main characters have to get? The big ten? Even The Big Chill
stopped at eight main characters.
There's a difference between the universe overall being reasonably balanced and the characters shown on screen being more males than females. What the camera focuses on is just a cross section of the larger whole. It's always going to be an uphill battle, in terms of gender balance in the characters shown on screen, because of the source material. I haven't seen any convincing evidence that the universe itself is "in no way balanced". (I think these last two points have been made on the BBS before.)
Yeah, I felt that Chekov was totally superfluous in both movies. I would have been far happier if they had stuck with one of the women and then introduced Chekov further down the line at a more age-appropriate point. Anton is great fun but it looks like they really struggled to use him in any way that was recognisable for his character.
I'm not down on wives, mothers, & girlfriends any more than I'm down on nurses. I just raise my voice at the lack of imagination when such a high proportion of the women are defined primarily in that role. I do give Amanda a pass as I think she signified more than that though.
In Trek 09 I had a quick glance at the cast list and ignoring the big 7, we had 50 men and 21 women. The men include an actress playing a male alien. The women include 4 wives/mothers/girlfriends, 2 medical staff, 2 silent Vulcan women among a larger number of Vulcan men, a stenographer, and a Romulan comms officer - even Romulans like lady secretaries! The women are not used imaginatively at all!