Yeah, no. If they want to be OP, make them mod for OP-ness. And the idea that mages should be OP demigods? Why do you think WOTC nerfed them so heavily in 4 and 5e? Because I'm pretty sure they weren't meant to be that, or people were just finding them unfun as fuck.
Also, struggling to do something as one class while another can do it with just the flick of a wrist, with no way of knowing which is which is not fun in my opinion. It's just stupid game design. Gaming as power fantasy has never appealed to me in the least (well, at least not since I turned thirteen, but at that point things were easing off in my life, so I wanted more challenge).
As long as there are many OP options, and the multiclass in 5e allows for that, it is way more fun than everyone being "equal" which equals boring.
If you wanna a good a example, just play Diablo 2. Every class in that game can become OP.
