I think what was said, if I may put words in @mamba 's mouth, is that D&D was so in its infancy that the choices of disunified mechanics were not good ones and had no chance to be.You realize your claim here is that anyone who doesn't think a universal mechanic like 3e-5e is better than what was done before (or anywhere else, for that matter) is objectively wrong? That's what you want to say here?
Not that having several different mechanics is bad. Just the ones chosen were not good or arbitrary or different for no reason/logic.