It's actually kind of funny, because OKW is not nearly as OP as every one makes it out to be, but it sure as fuck isn't the weakest faction. That award goes to Ostheer.
To be sure.
OKW is good in team games because they last long enough to get the late game abilities and high vet where they really shine; there are more resources anyway; you can generally rely on having an Ostheer player to get caches up so they offset their fuel starvation and there is more juicy salvage.
I won't talk on 1v1 because that's not my thing, but I've seen the tournament stats like everyone else