The balance idea never made a lot of sense considering that anyone at any time might choose to become a dark Jedi. The hubris of the old council overlooking the rise of Palpatine had to happen somehow of course, but the PT just feels contrived and makes them look like a bunch of old stoners (even before all those parodies). Beyond all that Chosen One plots are just the worst. TLJ at least did a reasonable job of look at the golden age with a sceptical eye, but even mentioning that period or any PT stuff was probably a mistake.
Why was mentioning the prequels a bad idea? Like it or not, they’re a part of Star Wars. You can’t just ignore them without making the saga feel incomplete. You may think the prequels are irredeemably bad and get angry whenever someone mentions them, but a lot of people think there were some parts that were good. TROS shows that trying to please a minor contingent of hardcore haters is almost never a good idea.