> For us 8 to 17 was tough due to a lot of things you weren’t supposed to be using going away (sun packages). But TONS of libraries did it anyway.

AFAIK, these libraries did so because there was no alternative, and some of the changes in Java 9 and later were done to provide them with an alternative. The only thing left is Signal/SignalHandler, which AFAIK still has no alternative outside the sun.* packages.