The next level of Pokemon comes down to prediction, anticipation, and choice. Teams can win at lower levels, but at the top, just having a powerful team doesn't guarantee a win. Smart team choice, using Pokemon that fit your playstyle, and scheme and accurate predictions are key.
Anticipation has been downplayed, with the addition of team preview, but you still need to feel out your opponent. Knowing what kind of set your opponent is running on his Pokemon is a massive advantage, that you can induce from seeing what their other Pokemon run.