DS9 offers a unique experience, where Roddenberry's idyllic future is pretty much BS and it pulls no punches stating that. At times, TOS and TNG wear a dunce cap while it expounds on how enlightened humanity has become, but the cracks in the writing betray just how sexist/racist/arrogant we still are.
Oh, I don't think that's entirely fair. DS9 doesn't displace the utopianism as much as it explores achieving it, maintaining it, and recognizing its limits. That could not have happened if there hadn't been a certain amount of lore that preceded it.