Someone who is so blatantly OP that you can clearly see they no longer have any room to grow. Even Goku and Vegeta run into troubles time and time again, despite how strong they are. Some manga simply start with MC(s) with absolutely godly unbeatable power and nothing can be a threat to them them anymore. Another problem is if they are so "perfect" and flawless that they know and have the solution to everything. Some slice of life can work with this to some extent, but I'm still not a big fan of this kind of character. It probably appeals to the "ALPHA MALES INTERNET BRIGADE FUCK YEAH" kind of people, but it's not something I find very entertaining. The whole "alpha/beta/simp/chad" is a recent trend that millenials sucked into, and I just never bought it. Hell, I imagine Naruto and Goku in the early days would be called similar names if they were released today.
I don't care if the MC is a weak male or female. If that's not the kind of protag you are into, kindly just find something else to read. There's something out there for everyone. Why bother coming back every time a new chapter comes out and moan about the MC being imperfect? I'm used to seeing weak protags like Nobita from Doraemon, or Pop from Dragon Quest, and despite how they can be annoying sometimes, they still help the story progress and I still find them entertaining.
To me, a good protag is not someone who is strong or weak, but how he or she helps the story progress.
There are two recent examples of bad protag that comes to my mind right now:
- A manga about this dude who got absurd ability to become stronger by sleeping. He trains every now and then, but still gets stronger by sleeping. Gods and demons started coming after him. Lo and behold, he defeats them with ease, using abilities that came out of absolutely nowhere.
- That female MC who got raped in Shounen A. Instead of facing her own problems and speaking up, she swept everything under the rug, even if that means destroying the life of the boy who saved her. Worst thing is she never did anything to help, so basically, she never grew at all. Not sure if she even counted as an MC or not... Well, the whole manga requires too much suspension of disbeliefs anyway, so not like it matters much.