The lack of hardware sprites was easily overcome by the raw speed of the spectrums CPU. Also at anything other than sprite focused games, ie vector graphics or the like the Spectrum smoked the C64. And even with sprites the C64 hardware was limited to 8 before you had to do strange multiplexing.
Sound wise the C64 was better but in terms of speed the Spectrum dominated.
I didn't say what was best, I said that comparing "only" MHz is missing part of the picture. Today machines are easier to compare because they have similar functionality, but back in the day it was different.
I had a ZX Spectrum +2A back in the day and I've programmed several games for the speccy, and the attribute clash was a pain :)
Sound wise the C64 was better but in terms of speed the Spectrum dominated.