That's more of a communication thing.
While I get your point, it's only when I see a top level pro stream or talk in an interview about their favorite champs that I realize how big a difference there is between being 'good' with a champ and really mastering them. Best example I ever saw, was Froggen was asked about Anivia's attack animation being so slow/unresponsive and that Riot was thinking about fixing it. He said that would be horrible, as the delay allows him to attack an enemy while laning and get out of minion attack range before it hits and avoiding their aggro/attack damage. That small advantage would allow him to harass them into range for a Q/E combo to kill them, which is one of the many reasons he's so feared on Anivia, just his total mastery of all the quirks relating to that champ. He's taken one of her worst disadvantages, her horrible attack animation, and turned it into an advantage when he plays that champ.
Another example, but not quite as good, was when I was watching Voyboy's stream and saw how he'd play Katarina top. I had thought of myself as a decent kat player before, but didn't even realize the mistakes I was making until I saw him playing her and building her tanky in mid game. He explained that her living longer in a teamfight increased the chance you end up getting a reset, which does so much more damage then one extra damage item would have done without a reset, and it made so much sense I almost face palmed myself for not seeing it before. Building a melee character as a total glass cannon is rarely a good idea, and while you want enough damage to get kills, getting a randuins/warmogs as a 2nd/3rd item ends up adding more damage over the course of a teamfight then something like a deathcap or void staff (at that point in the game). An early sorc boots and haunting guise, then a tanky item when you get out of laning, basically.
Point is, yes, teamwork and communication is important. But, until everyone on your team has 'mastered' their role, you have room to improve individually. Then, it's about knowing your teammates tendencies without having to say anything. Anyone who thinks they don't have room to improve is lying to themselves. Even top tier challenger players think they have room to improve.