I think it was necessary to have some bullies along the way for the 'heroes' to defeat -- it's a way to get people cheering for them, after all, and it's always satisfying to see bad guys get their comeuppence.

I saw the anime long before reading the manga, so my first impressions of everyone came from there. I liked Momo a lot, he seemed so good-natured and easy-going, with a kind of big brother attitude toward the younger kids (who were already getting a hard time from Arai and others, so Momo was refreshing.)