Slaying and being a good team player go hand in hand IMO. An inability to kill people efficiently means you're not gonna get the objective done. There are of course cases where the kid who goes 3-22 gets 2 caps in a CTF game, but that's very atypical and usually means their teammates are picking up the slaying slack and clearing the way for the caps. Same for the guy who goes 30-8 in a CTF game, they're usually holding down power weapons and putting on an immense amount of pressure on the enemy and a lot of cover for their teammates. Of course, there's outliers where there's the asshole who only slays and won't even return or grab a flag if it means getting out of their favorite position, but I think that type of player is not that common, it definitely happens, but most players who can kill very efficiently are good players who want to help the team win.
I just wish they put like 25% into personal, 75% into team winning to advance ranks.
Why's that? Because I occasionally play Halo solo?