The question becomes: Was the 3.X wizard only fun because it was overpowered? Or, at the very least, was the difference in fun between the 3e and 4e wizard because it was overpowered?
Because if that is true, then it is, to at least some extent, a good thing that the 4e wizard was less fun. "I'm more powerful than you and that is why I'm having fun" is not compatible with a teamwork-focused gameplay experience, because even when both sides mean well, it leads to "Angel Summoner and BMX Bandit."
Of course, I mostly just take Mr. Heinsoo at his word from that interview he gave a while back (I can dig up a Wayback link if you really need it.) He said that he was constantly having to fight against the dev team making the Wizard slightly stronger than every other class, and thus erred on the side of underpowered--but that combined with the scattered, unfocused nature of the Controller role meant that Wizard felt very weak (even though it was only very slightly weak) AND purposeless (even though it totally had a purpose, it was just much more subtle and variable.)
But surely there must be happier mediums that avoid it being a choice between Casters & Caddies, aka the choice between being a mundane and being a "god character" as was explicitly said upthread.