While I'm not going to allow myself to get dragged into a Coutinho vs Oscar slanging match (I think both have a lot of room for improvement but the potential is clearly there), there's a few things that are probably worth mentioning.
Stats aren't everything, I agree with that.
Mignolet has more clean sheets than DDG playing behind a defence with Glen Johnson in it. Is he a better keeper? Yes... Alright, no, but you were mad for a second, right?
Oscar might not be the star he was last season or the season before, but he's playing in a great team and struggling to stand out. It's a lot easier for Coutinho to stand out playing alongside makeshift strikers and midfielders like Joe Allen than it is for Oscar to stand out playing behind Costa & alongside Hazard & Fabregas.
I wouldn't trade, though. Not because I think Coutinho is better, but because I just enjoy watching him play more than I do Oscar or even Ozil.