Brother or no brother, he could still have kneecapped Sybok with the rock gun. I thought the brother angle was really lame, and prefer to think of Sybok just as Spock's onetime guru. The bro bit works for me mainly for Kirk's "I had a brother once" line, as it reinforces the notion of the family you create out of friendship can be a truer one than blood lines (then again, I'm an only child of an only child, and don't like much of the family I DO have, so of course I'm going to take that TOS/CHEERS view of friends&family.)
Also, I'm one of the rare folk who really like TFF, and I don't think cosmetic alterations will change my opinion of the film drastically (except in the way remastered added a cartoony element to FX, which I found objectionable.) The character stuff largely works for me, and it feels like TOS. I like some of the art direction, but find a lot of the VFX unsuccessful -- which is also like TOS to a degree.