You know Hajime no Ippo is not the same manga it was in yesteryear but, it is something to see so many people still so invested in it to this day.
Hardly invested if they're reading it on a pirate site and are doing it out of habit.
I'm also puzzled by this development because there wasn't much setup (despite yes, a year of this arc) and it looked as if for once Morikawa was going to ditch his usual theme of talent winning out and the world being unfair. It's not typical shonen fare and never has been.
One thing I would note though, is if Rosario really is just losing because he's out of shape, then it doesn't have much meaning for Mashiba to win now. Losing sucks just as much against an unprepared fighter, but thematically, it certainly wouldn't make sense to win either.
But people getting this mad and saying they won't support the manga anymore is even more puzzling to me. Because they'll be back next arc complaining about something else again, talking about dropping this "garbage" and how Morikawa has wasted another year or something. That's laughable to me, I've been reading this for about 25 years now, with about 30 volumes in ownership, this is nothing, and I see the same old type of commentators every generation giving their same worthless two cents in the comment section of a pirate site/group page.
No offense to those who are actually invested and/or have a cautious take, even if still a bit mad at the development. But you know you're in the minority.