Best of 5 MP question
 

Can someone verify that you get only 1 win towards your achievement if you win 3 out 5 rounds?
I've won a couple of rounds in one such game, but it didn't add any wins onto my leaderboard.
If so, than playing this is a waste of time, as you can actually play 3 - 5 single games instead.

That's correct mate. The out of 5 only counts as 1 win. The only achievement you really need to play best out of 5 for is the achievement Not so sneaky.