No one comes back years later with a Time Turner and wrecks havoc

Fuck I hate her bullshit inconsistency with this. Prior to that shitty play coming out I could have given you a simple explanation for this. First: the time turners were all made inoperable during book 5 when the team went to the Ministry. This was shown explicitly in the text (and is an example of Rowling’s delayed reaction to criticism that I think the Shaun video brings up). It could be bypassed pretty easily if you wanted, but it also works well enough to explain why nobody else uses one anymore, for a kid’s book.

But more crucially, the way time turners work in the original is pretty clear: it’s a one-way trip back in time. In book 3 they travel back a matter of hours, and then work back to the "present" in real time. You can’t use it to go back and kill Hitler or something like that, unless you want to be permanently stuck in the past. It’s never said, but it’s feasible that it could have been expanded on by placing a hard limit on how far back you can go at all. Then she went and wrote the play and (supposedly—I never read or watched it myself) completely broke all of that. I suppose you could be generous and say she was following Sanderson’s 3rd law, but IMO it wasn’t so much "expanding" on what she already had as it was "completely retconning the way it works in a way that also undermines previously-established plots".