Marvel: Contest of Champions: Is PVP real?
From what I've found, Marvel: Contest of Champions uses an asynchronous PVP system. This means that you are fighting AI using real opponents' characters. You can see this by the simple fact that you can pause the game during a fight and when you unpause, nothing has happened in your absence.
See this article:
In Contest’s “Versus” mode, you are technically playing other players – but it is really you playing AI using another team’s players.