Ippo references or cribs from Joe quite a lot, other than the stuff already mentioned. Like Takamura eating a tomato a day to diet like Rikiishi, one of the characters being essentially Joe with a kansai accent, the world champion being a pretty blatant expy of the world champ from Joe.
But if we're really to compare them generally then Joe just has much more substance. At the end of the day Ippo is for the most part a feel-good sports manga that tends to settle into a status quo and repeatedly reset to it for hundreds of chapters at a time, and most of it consists of throwing a kid with no personality in a boxing ring to win over and over again. Ashita no Joe is a study of a very complex character whose circumstances and psychology are constantly changing and evolving, gets into things like philosophy of life, and for as much as Joe finds meaning through picking up boxing it's much more upfront about him having to grapple with the destruction and even death that boxing can bring into people's lives. It's also a social commentary born from the social inequality that was lying underneath the perceived prosperity of Japan in the 1960s, where boxing doubles as a mirror against this (Joe feeling like he can get somewhere by embracing the rules of boxing whereas society remains unfair to Joe even if he conforms better to its rules and customs). Ippo is decidedly not this thoughtful.
Joe by the end has transformed from a brash juvenile delinquent to a quieter, more empathetic and more thoughtful man harboring a lot of guilt and alienation. Ippo's biggest problems are being upset about not winning a fight, and later quitting boxing and being worried about punch-drunk syndrome, both of which are things Joe did too, but with more nuanced context and a less one-note character, and without spending hundreds of chapters at a time teasing and blueballing the audience on the story going anywhere and endlessly repeating the same handful of scenes that never lead anywhere.
If we're looking at the art, just because Ippo's art has more detailed rendering doesn't inherently make it better. Chiba Tetsuya's art is clean, efficient, panels are well-blocked and composed, very readable. Ippo's action is notorious for how unreadable it becomes as the manga goes on; it's hard to believe but it was more than a decade ago that people started meming on the french fries flying around the ring all the time.
And if we're talking about the anime adaptations, b
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