I fought a Flash player yesterday, and it was pretty even. I got him at range on Atlantis and started zoning him out pretty well though, shooting him off the pipe, then using it myself when he'd elbow launch in. He ended up ragequitting and sending me a message that just said "garbage."
Got randomly matched up with him about 10 minutes later, and he picked Batman apparently to counter my Stroke. That time I played hard pressure on him (flying ninja, meaty 50/50s, etc.) and only really ever shot him with low guns to punish grapple. He played out the full match that time, which wasn't as close as the Flash one, but then send me another message saying "shits annoying dude."
I was a little stumped since I didn't even zone him, so I sent him a reply pointing that out. He said "sword spin, guns, why don't you play a real character?"
Clearly the guy just really hates the very concept of Deathstroke.