My experience with superhero games (which stretches back to 1994 and games like Superhero MUX, MetaMux, the original Project Infinity, etc) is that we "won" by telling a good narrative that would lead to future RP. More often than not that meant the hero somehow "lost" the fight because if we "won" then the villain would be locked up and unable to RP any more.
We also built our own sense of drama and tension by, again, telling a cooperative story. The nail biting tension came not from a dice roll but from waiting to see how our RP partners were going to respond to our poses and how we would respond in kind. Again, telling those thrilling narratives was how we won.
Winning did not come from having better dice rolls or having a more tactically built character. It came from experiencing rewarding RP and telling thrilling, action packed stories.
That said I still think using a structured game system has a place in these consent based narrative games. I hated having to read through 10 pages of crap to find out what my partners were capable of...and most of the time these long winded descriptions were so vague I was still left wondering. Character sheets provide an at a glance look at what a character is capable of. Looking at a M&M +sheet tells me just about everything I need to know about a character's capabilities and limits. We do not need to be shackled to the fickle whim of a D20 to guide our RP, however. Though I do think it is also still a viable option for people who do like to go that route so long as everyone in the scene is comfortable with it.
My experience on WoD games is that people are more invested in their characters and "losing" a fight is in some way a personal affront to them. It could also mean PK for not other reason than this person wanted to PK someone tonight. It is one of the reasons I quit WOD games entirely.