Does everyone else hate Mario's Up Smash? Ally just 3-0 6WX. Maybe Sonic is now middle tier. I haven't been able to win anything and now 6WX is getting rekt on using Sonic. The Sonic speed has met is end?
You would hate Luigi, Dr. Mario, Mr. Game & Watch, and Rosalina's Up Smashes. The issues with those moves having invincibility is that there's little end lag. Mr. Game & Watch acts at frame 39, Mario, Dr. Mario, and Luigi act at frame 40, and Rosalina at frame 48. They're all partially invincible on their hit frames; Mario's invincible from frames 9-12, Dr. Mario and Luigi's invincible from frames 9-13. Only Rosalina's and Mr. G&W are different; Rosie's from frames 7-19 which is 1 frame earlier from her frame 8 Up Smash and Mr. G&W's frame 24-25, but it's invincible from frames 4-25. In contrast, Wario's Up Smash and Wii Fit Trainer get to act at frame 58 and Roy at frame 59. Wario's frame 11-13 and invincible frames 8-14, WFT's frame 14-22 and invincible frames 12-15 ending at the clean hit of frames 12-15, and Roy's frame 12-23 and invincible frames 10-23.
Also, you not winning anything has nothing to do with Sonic's placement and 6wX seems to be dropping off in comparison to StaticManny. Whether that's a lack of practice or "optimal" play, I don't know. Calling Sonic a mid tier would be like calling Captain Falcon a low tier. For their tools to be called mid or low tier would mean there is a really, really high ceiling for good tools.
Edit: I just noticed that 6wX gets killed by trying to kill up top like that a lot. Dabuz has done this several times and Ally just did it.
And that is why Mario Up-B being Frame 3 invincible is one of the most boneheaded design choices in this game. Invincible Frame 8 Usmash comes close.
Invincible "Up Specials" are a common thing in fighting games. As anti-airs, they need something to challenge safely. Without invincibility or armor, you would have to anti-air by hitting before your opponent does - Falco's Side Smash is an example of this as it lacks any invincibility and is frame 17, but makes up for being transcendent allowing him to challenge anything, arcing over his head, and moves him forward or his angled up Ftilt being fast enough of a poke to interrupt aerial approaches. Famously, Shoryuken is invincible upon startup and it's a notorious anti-air. Anti-airs are generally fast and invincible. Shoruken's frame 6 in Smash 4 and in KoF XIII, Kyo's Oniyaki is frame 4 for the light and EX version or frame 7 for the fierce version. Mario's 3 Super Jump Punch might be pushing or not... Frame 6 is enough to get interrupt many things. They are, however, countered by the fact you're in the air. That means you have to land.
Here's the only issue: Smash's Up Specials aren't universal. Little Mac's Rising Uppercut for example has no armor nor any invincibility for either the ground or air version and Roy's Blazer only has armor on the ground while Marth, Lucina, and Sonic have invincible frames even though Sonic's isn't an (normal) attack. In other cases, Up Specials are strictly for travel like Rosalina's Launch Star or the Pits' Gift of Flight. For those that don't have any armor like Zelda, Shulk, or Link, then they'll need to hit first, but intercepting an anti-air would be difficult for Zelda's Farore's Wind not to mention she could just SD and Link's Spin Attack is kind of worthless for vertical challenging. Oh, and for some, their Up Specials are just inferior versions of other characters. By some, I mean Falco.
I don't remember high BKB moves killing as low as they do now in previous games, even without rage. It didn't look like Sonic should have died there tbh. I've seen Game & Watch get killed by Mario's Up-B at stage-level, but rage and smash charge vulnerability factored into that too.
Mario's Super Jump Punch doesn't even have base knockback until the last, sixth hit. For the first 5 hits, they only have weighted knockback and 100 knockback growth which shouldn't be doing anything... I think. Peach and Roy are also capable of doing this with her Parasol and his Blazer. And you guessed it! Both Parasol and Blazer have weighted knockback for their looping hits. Why it's doing this, I don't know. Samus, Little Mac, and Fox can't do this with their Screw Attack, Rising Uppercut, and Uair. I'm going to assume because they're purely vertical moves that prevent this - you'll just fall out instead of being forced up - weird interaction as SJP, Parasol, and Blazer are all diagonally-moving moves.