Not sure where you are going with this but the issue with your argument is that there is only 1 max park. Everyone else out there still needs a half-decent 3x3 stage and with the limitations of roux on big cubes, 9/10 times CFOP will be the better option. I'm not saying that M moves are impossible on 5-7, I'm saying they are much harder than regular moves done in a CFOP, ZZ, or Petrus solve. Not to mention that M moves are very risky on big cubes and I got a 5x5 DNF that was going to be a PR due to an MU U perm that was an r off from being solved.