Even though the nerf to MK's up aerial took away his best punish, I still believe he is somewhere between 5-10, and is definitely still top-tier.
What does MK have?
-Good neutral game: mobility, disjointed range, and attack speed will always ensure a good neutral game.
MK's fair has 4 less frames of landing lag (20->16, one more frame than Brawl, though Brawl's auto-cancelled in a short-hop), and has always had a 2.0 hitlag modifier (which benefits from shield mechanics), and surprisingly has longer range than in Brawl (last hit 5.0->6.5, which is significant). It's now -13 on shield, and this isn't counting shield-drop (-6) or jumpsquat(-9 vs 4 frame jumpsquat). Spaced at max range, MK's fair is now safe on shield, which is a big plus: one of MK's issues with his approach is that he had no quick, safe long-ranged move that hit in front of him. Now he does. And guess what? Fair -> dash attack is a true combo at lower percents. MK now has a safe aerial poke that also leads into other moves.
Of course, he has that in addition to dash attack, dash grab, dair, d tilt, and f tilt.
MK previously had two major issues in neutral:
1) lack of a projectile
2) all his aerials were unsafe on landing
The second has been largely remedied, and now gives him more mix-up potential with his approach.
On an important note, MK has a somewhat easier time in neutral vs Sheik thanks to the needle and fair nerfs, though he still loses pretty badly. I'd imagine the Sheik MU isn't so terrible anymore (55-45 is actually plausible in theory, though we need proof), because Sheik's neutral game has been worsened (still pretty dope though), while MK's has been notably improved. MK still goes even or beats her in KOing ability even without the staircase, because now her 50/50 has been tightened, and she can't tack on damage with needles until her fair KO's.
is still considered positive for MK, and the fact that she's becoming more relevant is actually a plus. I'd argue that MK's OVERALL MU spread is better than pre-patch, because the one hard-counter he had is now up for debate.
-Advantage state: yes, the uair nerf was a major thing. What did the nerf do? It took away the ability to chain it into itself to drag opponents off the top of the screen. But the nerf didn't butcher its combo potential. It can still footstool at lower percents, and can combo into his other aerials until mid-percents, as well as Tornado and SL. The nerf specifically took away (not completely) its
KO CONFIRMS, it's still one of his best combo moves.
MK still has very good KOing ability. The decreased lag on fair allows tech-chases from mid to high percents. DA into SL is still a thing. SL is still good OoS, up smash is frame 8 and kills reasonably, and f smash is safe. Up throw and back throw act as stock caps, meaning you generally aren't safe holding shield. MK players: don't let the loss of the up air combo blind you from the fact that he can still rack up damage and KO.
MK has his edge-guarding: a frame 7 bair with dumb knockback, frame 9 fair with good range, frame 4 dair that semi-spikes, and frame 6 nair that lingers and kills when clean. And all these moves make for easy, effective air dodge punishes.
-Disadvantage: 5 midair jumps make him virtually untouchable offstage, and give him great defense against juggles combined with a frame 4 down air and Cape for mix-ups.
TL;DR while the up air nerf IS a major thing, post-patch MK is more well-rounded as a character. He's strong in neutral, and still dominates in advantage, and has a very good disadvantage. He still has more than what it takes to be top-tier.