a) It's allways your fault !!

b) Used KS should have no effect on the created disks, and even if a game is incompatible it would just crash AFTER starting to boot.
c) my money is on a misaligned/faulty floppy. Any other floppy/Amiga at hand ? Any disks that do boot ?
A1200 "best" Amiga ?? Not in my book ..... it is the most sensible solution if you want to run games on real HW with WHDLoad (after you added an 030-accel that is) but for everything else there are better choices.