I'm curious to which games you refer to though, because he was legitimately bad for the entire ECF. He was also very up and down against Boston/Philly. LeBron has had a few bad games each series but overall has been the Heat's best player in the playoffs.
Wade's just been better in the Finals.
I don't think Wade was that up-and-down against the Celts. His worst game that series was 23 points, 6 rebounds, 7 assists on 42% shooting.
He was mediocre in Games 1 and 2 against Philly, and he struggled in Games 3 through 5 in Miami (although I wouldn't call him legitimately bad).
On balance, though, Wade has been very good. He is the Heat's leading scorer, and he leads the team in FG%, eFG%, TS%, and PER. He is virtually tied with Lebron in terms of TRB% and AST%, and has a slightly lower TOV%.
I think there's a very strong argument that Wade has been the Heat's best overall player during the course of the playoffs, with Lebron very slightly behind.