It might just boil down to feel.
A high level 3.5 wizard felt epic!
A high level 5e wizard is a bad ass, to be sure, and is absolutely worth playing, but not in the same league as his 3.5 counterpart.
And that's not a bad thing in the context of this edition. As many have already said, the 5E wizard is much more of a team player now.
The last character I played before 5E was a 3.5 wizard that made it to 20th level. And that guy could do some pretty amazing things. So when I first started in a 5E game, I immediately rolled up a wizard... and was immediately disappointed. When I put the class under a microscope and really dug into the spells, it was obvious that my new wizard was never going to be able to pull off the stunts that his predecessor had. Concentration?! What is this crap?! You're telling me I can't fly and be invisible at the same time?! Are you kidding me?! And I get one measly 9th level spell?! And Teleport is suddenly 7th level? How am I supposed to zap the party from one side of the kingdom to the other?!
But then, as the game progressed, I began to see the elegance in the system. At low levels the at will cantrips were so great! And the school specializations, well that was pretty sweet. And that d6 hit dice was nothing to sneeze at! And the more I tinkered with the new spell versions the more I found things to like. Familiar suddenly gave me a lot more options without the constant terror of my familiar getting killed and all the headaches that that used to entail. And Fireball started right out the gate at 8d6 damage; what's not to like about that? Sure, the every round save chances on spells like Hold Person was kind of a drag, but it also meant that my fighter companions wouldn't be taken out of whole combats like they used to, so not a bad trade off, really. And sure, I couldn't stack a lot of spells, but the memory of some high level 3.5 sessions when it took, literally, twenty to thirty minutes just to figure out which buffs needed to be cast in which order on how many allies, etc. made me actually appreciate not ever having to do that again. And no, I wasn't tossing out huge levels of damage, but a Haste here, or a Wall of Force there, was suddenly the difference between winning and losing a combat.
The point is, I was still plenty useful, and in the context of the system, it seemed balanced and right.
That wizard didn't make it into the higher levels, but then I started to DM, and the system made even more sense. The current wizard in our party is 14th level, and he's still not breaking the game. He's got Teleport now, but it's easier to manage. He still puts out plenty of DPR (he's an evoker), but not as much as the barbarian. He does a little battlefield control, takes out the mobs of little guys, softens up the bigger baddies, and he can Fireball to his heart's content while excluding his own party members, which is exactly as awesome as it sounds. He's useful and contributes while helping the other party members to be useful and contribute, and that's kind of what it's all about.
And on the flip side, I can now whip up a high level caster bad guy without pulling my hair out trying to figure out their catalog of spell, the umpteen buffs they'll have on them, and what metamagics they'll be using. In short, it is much easier to DM.
There's things I still miss about 3.5, and, all things being equal, if I had to choose, I might play a 3.5 wizard over a 5E. As a 5E wizard you're probably never going to be Merlin. You're probably never going to build a floating castle. You're probably never going to craft your own Staff of Butt Kicking.
But, that said, I'd rather play in a 5E game, and I'd have no problem playing a wizard in that game.
and if I had to choose which wizard to DM? No contest. 5E all the way.