Sorry for DD post, but I have to...
It seems the Metacritic has retrieved the score and now it's 91 for PC, 90 for PS4, and 92 for Xbox One. So if it comes to score, Overwatch and Smash Wii U are both equally awesome.
However, Smash Wii U still lose to Overwatch on Game Informer and Destructriod's score. But Smash Wii U is still beats Overwatch on IGN's score only by 0.4 score.
Yes, both games outscores each other only with minimum on many game reviewing sites. So both games are all equally great as a Multiplayer game.
However, one thing that I personally think Overwatch did better than Smash Wii U is how they promote the game by releasing animate shorts. True that Smash 4 have character trailers, but that's pretty much it. Since they don't make Story mode cutscenes because they brag about them being leaked online. Why not just officially make those cutscenes or animate shorts and post on Youtube as promoting the game?
But one thing that Smash Wii U totally beats Overwatch, has to be it's soundtrack. Overwatch's OST sounds awesome. But Smash Wii U has like over 500+ OST from all of the Nintendo's iconic franchise. And yeah Blizzard is not a game company where their games are famous for awesome OST. But this is actually why I love Nintendo games the most, their OST are just epic.