His play later in the game was a big reason for the win, his play earlier one of the reasons they were down. I was impressed how he came back against the best defense after struggling for such a long time in the game. Only other QB I'd count on to be able to do this would be Wilson. On the other hand you had Jimmy G who heavily benefited from the run game again and didn't have to create anything special himself to get the lead, being "average" was enough. When he was asked to do more...well we all have seen what happened and he didn't have to play a #1 defense, he played an overall average defense that defends the pass well.
There are plenty of reasons for the Chiefs win and some were not even in their hand (Jimmy G, Shanahan, fortunate ref decisions), games like these are why I really don't care about Finals MVP shit. Like mentioned itt they could have easily given it to Williams or Jones as well.