Sure, but that looks to me like the issues didn't actually need to be solved.
Except to reach that conclusion, you'd have to ignore everything up to said conclusion.
I mean, if they just stopped talking about Voldemort halfway through book 7 and the victory was getting rights for house elves, you'd not assume that Voldemort was defeated off screen, would you?
No, but that would be terrible writing.
Voldemort is an existential threat, was introduced as a threat from ch. 1 of book 1, and his shadow hung over the entire series. House elves weren't even introduced until the second book, and came in and out of prominence. This would basically require going back to the beginning.
"Saving the world" should have come with fixing or working to fix those issues and it didn't happen. Like, shonen fighting anime for children manages to pull this stuff off on a regular basis.
When kids/YA books bring up these sorts of problems, saving the day usually involves taking major steps to solving those problems. The non-human discrimination, the rift between goblins and wizards, the whole slavery thing, etc. Harry Potter was such a special boy he solved the problem without having to fix any of the underlying issues.
I can't comment on shonen, but I can comment on JF/YA. And I completely disagree.
First, I can cite plenty of works where problems exist within a setting, and those problems aren't solved by the end of the main sequence. Off the top of my head, these include A Series of Unfortunate Events, Artemis Fowl, arguably The Hunger Games, Percy Jackson, and Ready Player One. I can likewise cite works in this age range where all the major problems
are solved, but there's no rule in JF/YA that states this has to happen. Heck, there's no rule in any genre that says that this has to happen.
Second, Harry's in no position to fix these issues. He's only special by virtue of chance, there's no inherent ability he possesses that others don't, he's a jack of all trades in his skillset, the entire series runs its course before he's even a legal adult, he barely scrapes through in the end in defeating Voldemort, which is something that only happens because of the amount of support he was given. Harry isn't "the special," he's special only due to circumstance, which is presented as a tragedy. Your entire thesis would involve redoing the entire series from scratch.
Third, it doesn't change the fact that the above mentioned issues were solved canonically, or at least ameliorated.
Very slowly, after the story, super incrementally, and only because somebody wanted to write a sequel story. If Cursed Child didn't exist, Harry Potter wouldn't've addressed literally any of the systemic problems that lead to that singular line about the statue being bad. Hell, they kept Nazi House *and* the sorting hat that shuffles all the ambitious racists together.
You're conflating sources. Cursed Child doesn't touch on these things, because that isn't the story Cursed Child is telling. The stuff that happens over the time period in question was fleshed out via Pottormore, and there's no evidence that the worldbuilding and anciliary material was to prepare for Cursed Child.