Are you talking about maximum sharpness, or about AF ability? Does the M6 have a weaker (or absent) AA filter?
If AF, is the 7D2 in OVF focus mode, or sensor focus?
I mean in AF. I don't know about the AA filter.
The AF on the 7DII was OVF - phase detect, I was having a lot of trouble with the Avocet chicks and since the M6 is sensor AF and not too shabby (dual-pixel AF), I thought I'd give it a try. It did not work well for the sandpipers though (they were quicker), the 7DII OVF was much better for those.
my thoughts here in the M6 thread: