Dunno how active this thread is anymore but I've had my experience with fighting games on Steam ruined by the new update. Checking my input in Skullgirls training and the game won't read my UpBack or Downforward unless I mash the corner, so I can't reliably input those for movement/specials/supers. Checked my devices input tester and it had no problems, so I can't tell if the problem's somehow on Steam's end or my controller. I play on a Hori RAP4 and have had no problems with it until now. I tested inputs on Skullgirls, Them's Fightin' Herds, and GGXACPR and the problem was the same across all three.
Are you certain that it's a steam update causing it?