The main reason I argue that things like healing are homogenised is more to do with how they are balanced and to do with encounters. So much ends up being used in the same way and you can say list the AST and SCH equivalents of each core WHM skill. It ends up feeling very similar unless you're being pushed to properly use your toolkit.
And where different jobs had strengths and weaknesses over each other over time has blurred. Taking what I've said in another thread, I'd rather the idea of balance being about making what's strong about a job more worthwhile over what is weak and having means to compensate weakness through skill. Rather than having a level playing field of balance.