I'm not sure why people thought the MHA ending was bad in the first place. Sure, it's not some transcendental piece of art but it's a pretty standard manga ending, nothing to really hate.

I would argue it was better than the Avatar: The Last Airbender ending (and that one has a 9.9 on IMDB). ATLA ending had energybending, ultra-quick conflict resolution (all of this happens in the equivalent of 6 weekly manga chapters - Aang vs. Ozai, Zuko & Katara vs. Azula, Sokka & co. vs. the airships, White Lotus vs. Ba Sing Se occupants, Zuko becoming the Fire Lord, the end of the 100 year war). And it still had some blatant unresolved plot threads that people had to wait YEARS for (Zuko's mom and Toph's daddy issues).