Just curious... what brand has a pancake 22 f/2 in a DSLR form factor that you're trying to compare it to?Beyond the Canon EF-M 22mm F2 (does not work on 70D), there is APS-C lens Nikon 35mm F1.8 and Sigma 30mm F1.4 also.
Why not EF-S 22mm F2 ?
Nikon's 35 f/1.8 and Sigma's 30 f/1.4 aren't pancakes. The geometry (flange distance) for the M is different, so the focal length for a pancake is different as well.
You can't reason with these folks, it seems. They want everything. Small, fast, cheap, IS, with intelligent composition mode. I'm very close to just abandoning the time I waste on photography forums.