If this is your point you didn't say that. "the beginning was great, but the story should have been way way shorter" I don't know how else I am supposed to interpret this as anything other than "I think the story should have been shorter".
These kinds of revenge stories have a few staples and...
I'm gonna be honest this one of the shorter revenge mangas. Some revenge stories are long novels or hundreds of chapters long. This genre is filled with some massively long and complex stories. So I don't get the complaining about it being way too long and it being prolonged bullying.