The only reason people want him banned is because people think that he has no counters whatsoever, and destroys the variety because he has no counterpicks.
I feel that isn't the case at all. It's mostly because of people's laziness that proclaim that MetaKnight is the best counter for MetaKnight. This is not true at all, and just makes things worse. It's not because he has a better ratio, but rather it's basically determine on skill, and if your MetaKnight is better than the MetaKnight you are fighting, which most of the time is a no.
MetaKnight does have counters, and some character can actually counter him if you put in some effort. Infact, he even has a counterpick setup during his opponents counterpick. All you need to do is train a decent Yoshi, learn how to Pivot Grab, and use one of the many heavy counter stages he has. It will make the fight a hell of alot easier, even if your Yoshi is decent, then you can just revert back to your main or whoever you were using.
Everywhere I look now, there seems to be more people finding ways to deal with him. Jigglypuff, Olimar, Lucario's, and a few more characters are figuring out MetaKnight and how to deal with him. Fox mains now think that they have an even matchup against MetaKnight. Yoshi Mains are Figuring out new Tech's to make this fight slightly more easier. MetaKnight has weaknesses, yet people are just simply too lazy to figure out what they are.
MetaKnight is great, but he isn't god. He bleeds like everyone else.