Just my opinion, but I feel like these kind of sports are unbalanced, because our muscles are mostly powerful for legs, of course rowing is still using legs, but not much more than arms

If you have proper rowing form your arms are almost entirely used just for holding on. The majority of your power comes from legs and core.

Not a professional rower, just looked into form when I was using a rowing machine.

As mentioned you are wrong on this: rowing is mostly legs, some core muscle and then a little arm. As you don't have your full weight on your knees it is a good way to get started on working your legs when you're overweight.

As someone who rows an actual boat once or twice almost every other summer I just want to say that rowing is mostly upper body and arms, with little to no legwork.

I guess we're not thinking of the same thing when writing about rowing.

I'm thinking of this: https://en.wikipedia.org/wiki/Rowing_(sport)#/media/File:Avi... and if you do little legwork you're doing it wrong.

or it does when you're not rowing for time.