The player. Game 1, Curbo chooses Cage. Fine, it's his main. He loses. He then KEEPS WITH CAGE for one more game, going down 2-0. That's a foolish decision, and that is possibly what cost him the match. And decision making is part of player skill.REO vs Curbo was a good example of this topic.
REO was 2-0 up against Curbos Cage using his Kabal. Curbo switches to Jax, pulls it back 2-1. REO goes for Cage, and somehow Curbo wins again. This could be due to the fact that Curbos Cage is miles better than REO's, so he knows what he can and cant get away with, but ultimately REO sticks with Cage and grinds out a 3-2 victory.
So was it the player or the character that was better in their encounter?
Incidentally, REO also plays a pretty good Kenshi, whom he could've used had he known that Curbo might pick Jax.