Yeah that's sort of my concern. That's what happened in Reach's arena since it was based off individual performance. It's great if a teammate goes 30-4 in CTF if they're also helping to cover the flag, keep spawns in check, etc. But when they're going for kills because they want to be on top of the team leaderboard to rank up, that's bad.
CTF is actually a really good example. You would think that flag captures would be the most important thing in winning.
But when we analyze millions and millions of CTF matches, and see what stats are the most important to winning a match, it's not flag captures. It's killing and not dying. By at least 10 times.
Which I think makes sense because in order to cap a flag, you kind of have to first kill almost the entire other team without dying, maybe twice.
Of course, if you just sit there and kill and never grab the flag, that's not helpful, but that doesn't happen enough in real matches to matter. Instead, by far, the teams that slay the best win in flag.