I've been watching Federer play before he was ever number 1, and his topspin 1HBH has never been very consistent against better players, but I think it definitely has gotten worse over the years possibly due to lack of confidence. That's a fact that players on the tour learn to exploit over the years. He has shanked so many balls in his backhand side that it worries me when he try to hit his backhand now. That's why when you look at stats, Federer hits disproportional amount of inside out forehand compared to other players. Also he hits a huge amount of slices on the backhand side, but you can argue that it's for mixing the game up.
Wawrinka's topspin backhand is definitely more consistent and better than his forehand in many situations. So without a doubt in my mind, if Wawrinka has better 1HBH than Federer.