You absolutely aren’t wrong but it is a big step away from the comparison to spaghetti westerns. Avatar or RWBY is an American shonen in the same way that A Fistful of Dollars is an Italian western. Marvel is an American shonen in the same way that Seven Samurai is a Japanese western. In the former while some stylistic differences appear you could easily not be aware of the nation of origin until you learn the stylistic differences. In the latter you can’t mistake it. Seven Samurai is drenched in Japan like marvel is drenched in America. It’s easier to watch seven samurai and not know it’s a western than to not know it’s Japanese.