No matter how much you do in-game to try and help your teammates, it will fall short. The main component of teamwork is communication. Has been, always will be.
That's no fault of yours, by the way. It's actually still the fault of Trueskill, albeit indirectly. In Halo 3 people had a number next to their names that they cared about. They didn't want to lose their number. They had mics. They talked. They called out.
But in Reach, with no number, the reasons to talk faded away. People stopped caring. People stopped trying, except for the few with a full party, or the people, like you, who go in to still try and salvage what it used to be like to play Halo.
Unfortunately, that's not enough anymore.