K/D scrubs do it in Objective because they are too garbage to do it in TDM.
But, everyone paid for the game and are entitled to play how they choose. So if going for a 3 k/d through any means possible makes them happy, let them do it. Just be nice and think about how that player needs a high K/D to impress his imaginary cyber GF.
I'm an objective player who can work just as well in the 3 cap and hold system or the 2 cap system. Even I have never gotten 20 caps outside of maybe Clan Operations back in MW3 where nobody defended flags. I'm pretty sure 16 is my high any other time. So color me impressed by your effort even though I have to be depressed by your team since they sure didn't touch too many flags either. In fact, the other team put more effort into it than your team did. Anytime that I play with randoms, I expect to have to throw on the backpack if we are going to have a chance to win. Sometimes I get lucky and find some really good players on my team and other times I find myself having to do all of the work but it is what it is.
The biggest trouble with the 3 cap though is that a lot of folks can't handle it. That's something that you have to consider if you are playing for the win. My clan and I often will play the 2 cap long enough to get a lead going and then 3 cap for the rest of the match. But then again, we are an experienced team. The 3 cap in random lobbies is a dicey proposition as you just don't know who you've got to work with but if they are strong enough players it is the fastest way to win a DOM match. If they aren't the right players, its the fastest way to lose as well.
As to your theory, well yes that is why a lot of people play the 2 cap method in DOM. It's a proven system that yields predictable results. It makes getting those longer streaks much easier and as such will attract those that wish to go for them.
That's why I don't like objective modes. I play TDM almost exlusively (although lately I've been forced to play S&D by some of my friends.) It's funny I'll see some dudes with very high overall KDs and do terribly game after game in TDM. When I check to see what modes they play the most. It's usually an obj. mode like Dom.
Without an objective crutch, like in TDM, it really exposes how terrible some of these killwhores are.