The part where it sucked itself off for not killing All Might in the Iron Might fight is what really killed it for me, since like the entire situation did not need to happen, but it did because Hori loves MCU Iron Man (that was his actual reason afaik).
Realistically All Might should've died fighting All For One, he was basically out of the picture for Season 4 despite making a full recovery from his injuries (albeit being fully depowered).
Two options would've been viable at that point.
1. All Might dies; time skip moves everyone into the next year. Opportunity to shuffle up Class 1-A with Class 1-B and new characters (core characters wouldn't change but would provide a way to put some of Class 1-B's more interesting characters in the limelight while retiring the background characters).
2. All Might doesn't die, but his death is faked; with only Deku knowing that he isn't dead. Could be in a coma. Good way to put him out of the picture indefinitely while letting him see the fruits of his labor (Deku becoming a hero, etc.)
Characters like All Might usually die at the end of the first arc, especially at the hands of the villain. (There's a reason why
the "Mentor Occupational Hazard" article on TVTropes is so long, it's that common.
Keeping a character like All Might alive should've had a point, namely still having a role to play in the story (like seeing Deku become No. 1 hero and his true successor—which didn't happen) or just a general avoidance in killing people off (like which is what One Piece does). But seeing how Hori offed Midnight, Star & Stripe, Nighteye, several other one-scene heroes, and several villains he's clearly not averse to death.
The most infuriating part of all this is that by the time MHA was pulling all of these stunts audiences were starting to wise up to the "subverted expectations" gimmick. (
The Last Jedi was in December 2017). And like
The Last Jedi, these "subverted expectations" weren't fun or interesting. Instead it harmed beloved characters, pissed people off, and ruined the entire franchise.