Maybe the guy that is working his way towards the 11 killstreak in order to get the Gunship is actually on the losing team, in this case his Gunship could actually turn the match around based on the performance of this person alone. That's something a lot of us like about COD, the fact that even when you are on the losing team, you still stand a chance at doing well on your own or even at making your team win the match.
I'm not going to say COD's approach is better than others because this depends on personal preferences, but for those of us that prefer more of a "lone wolf" kind of play style, COD is better suited for us than, say, Halo (much more team based than COD, which might be a good thing for some, but not for others). And killstreaks, like I said, play a bit of a role in that.
Killstreaks were one of COD4's innovations to the genre, they add a new dynamic to the typical multiplayer FPS experience that is exciting and interesting. Personally, I would lose a bit of interest in the franchise if they got rid of killstreaks. I however agree with you on that it may need a revision in the way you obtain them. Perhaps they shouldn't even be "kill"streaks at all, at least depending on game mode. I don't have much of a complain in this regard because I always play TDM, anyway, but like many have complained over the years, it's ridiculous that people still get rewarded for their kills in objective game modes. How about giving rewards based on your performance when it comes to doing what the game mode you're playing is all about (capturing flags in Domination, planting/defusing in Search&Destroy, etc)? It baffles me that this hasn't been changed yet.
In any case, Black Ops has the Barebones playlists, which are killstreakless. If you hate the concept of killstreaks that much, you can always play that. Everyone is happy.