Earning 70 kills doesn't really prove anything. The 20+ defends are the only proof that their large amount of kills were helpful. Suppressing the enemy as many players say is often an excuse to preserve K/D stats. Why? Because when the life of the match hangs in the balance and you ask those players to help capture an objective, they will refuse. I've experienced this many times since I was playing COD4 in 2007.
Killstreaks can be helpful, but they can also be countered. For example, my team will often run with armor piercing, the MAAWS, and ground jammer. If a player earns kills without objective pursuits, only to have their earned assault streaks destroyed in a flash, that makes them useless.
Lastly, if kills and deaths mattered so much, then why can coordinated teams win Domination games without a single kill? Yes, it's possible, and it has happened many times before.
(This isn't my game, but this is an example)
~RUGGED SAVIOR