I don't think Ashita no Joe would be very controversial simply due the fact that boxing ain't that big of a deal to many people and their personal lives. Mangas, aka Imagination and Ideas how are are a big thing to anyone reading manga as a hobby and the thought of someone stealing someone else's work is rightly something to take offense at.
I honestly couldn't care less about the reason why the Japanese audience dislike this series. To me its real flaws lie not in its plagiarism, which is an interesting grey and black moral area, but the MC being outdone by Aino's character despite her few appearances, hardly any creation of a real character cast (the editors and assistants could have been one, but they were just there and then gone) outside of Teppei and Aino, the "mangaka" part being hardly mentioned compared to the timemachine part and ofc the timeskips just being lazy ways to get quickly to the results of the many storylines without actually seeing how those results really came to be.
Like show us why the Editors decided to have Anima be in 1st place for over thirty issues in a row, just that it is "good" cannot be reason enough, was it the people votes or their comments or what was it that made them give a new series the spotlight for over half a year? Show us how Teppei plans the battle scenes or story plottwists being revealed as in art choice, expected reader reaction, earlier hinting, etc. when he is on his own. Show us how important the work of the assistants actually is like it was done in Bakuman. Explain to us how and when a TOC ranking can be seen as influenced by readers and when by editors. Just DO something. Do something that makes us care for both of the characters, the story and ofc their own work, their manga creations. Because right now stuff is "just happening" because it does but it is not shown why or how it matters.
There is a lot this story could do better to be more interesting to me, personally, and plagiarism hardly is in the top ten of my worries about it. If other people see it differently, let them be. No reason to get worked up over something you cannot change anyway, Stivie, no reader in Japan will care about your expressed opinion here and the ones of us who does read it here have heard it many times already, so yeah, we get it, but if you wanna challenge that mindset, go to the Japanese boards with its many many TPG threads and defend the series over there in Japanese. Here it is just starting to annoy me to see you repeat yourself over and over again. I get you're upset about it but to act like the mangaka has no fault at what happened to this series is not doing it justice either. After all before the results of the first chapter and the readers impressions of it were told the mangaka should have already been at chapter 3 or 4 or 5 and the problems didn't start after those chapters but in my opinion right after the first chapter with Teppei having no friend as supporter who knows the same as he does, the whole mangaka tricks and ways of working not clearly shown or explained, the focus of Teppei's guilt over and over again to cast him in a sympathetic light when all he did was come across as annoying and hypocritical as he kept doing what he said he hated doing and other stuff I won't bother repeating.
Face it, the autor of this series had an interesting idea but he failed to capture his readers not only because some or many of them dislike the plagiarism but also due not creating a likeable MC, a memorable cast, an "endgoal" that wasn't just "I wanna create a manga everyone enjoys reading" from the start and so on. If it does get axed, which I hope it won't but it might, or if it gets finished by the mangaka earlier than intended because he was frustrated with the response to his work, then it can still work as a learning experience for him like the failed series did for Horikoshi until his hit of MHA: An interesting idea alone is not enough to create a successful series, it is just one part of it and his other parts to the idea were inadequate in my opinion.