The over specialization of the mundane classes didn't occur as the result of realism. It occurred as a result of failure to rectify bad design, which resulted in more bad design.
Yeah. Not sure I can articulate my thoughts on this. Maybe the problem is that over the years design issues have just sort of piled up without any meaningful attempt to fix them.
I have my own d20 that I play that fixes the issues I have with the game but such things only go so far as to help me make a game my friends and I enjoy. Maybe at the end of the day that's all it needs to be.