As others have said, he's nowhere close now. GRRM has sold the better part of 10 million books, Rothfuss is simply not in that league (though if I was told that TNotW had sold more than a million copies so far, I'd believe it), despite being the biggest epic fantasy debut for many years. Maybe a few years from now, if Rothfuss can increase his writing speed and catch up with GRRM. Rothfuss's first book is somewhat more approachable than AGoT and I think could win over a larger fanbase, but the likes of GRRM and Robert Jordan have huge head starts.
I dunno if ADWD, despite an even longer wait, will be bigger than WMF at this point. I may be wrong, but I think Rothfuss has surpassed Martin in terms of fans.