In terms of most impactful players the two obvious ones are b4nny and knoxxx for structuring a team around playing a specific way.
There are a few players who are extremely impactful mainly because they win every single dm fight, but who also understand the game well enough to not make that counterable. Mike on pocket and clockwork come to mind. I think clockwork might be the single most impactful player to have in a match when he's on just because he can consistently just walk over everyone if he wants to.
Stark is one of the most impactful players in the game right now, his mechanics are extremely solid and although he doesn't maincall he has some of the best gamesense I've ever seen in a player and always seems to be thinking steps ahead.
Oh and I forgot about Seagull, similar to Stark, incredibly smart player who contributed to his team through very competent mechanics and incredible gamesense but while being a flank class so not necessarily the primary caller.