I don’t think the show ever claimed for it to be a utopia, but they have no homelessness, hunger, etc. at least on Earth and member worlds. That doesn’t mean there isn’t that outside the Federation or on distant colonies which tend to be left to their own devices. For instance, Tasha Yar’s homeworld was a failed colony. We don’t know at what point it failed or if/when the Federation stepped in.

By DS9, it was bluntly stated that Earth was a utopia.

Stated bluntly? Surely you jest. Which episode? The closest I can recall is when Sisko, in an emotionally charged rant called it a “paradise” compared to the frontier. But that’s far from describing it as Utopia. And even then, that’s just Earth. Not the entire Federation.