Since Maxon also updates the ProjectTool when a new version of C4D comes out and it may have new flags or optimazations and changes to the project structure for XCode and Visual Studio.
From what I can tell it's pretty stable, also I don't mind what someone else thinks my compiler optimisation flags should be.
Maintaining your own CMake version going forward for R20, R21, S22, RXX etc... would be a massive pain and just slow you down.
Not as painful as you think it might be, also not as slow.
Whatever floats your boat. :)