> The things I mentioned (local symbol auto-complete, reference-chasing, global go-to-symbol) are things that modern code editors do by default for any programming language

Sure, they can. But as said, they are still quite basic stuff compared to what IDEs do. It's better than nothing, but they don't contribute to productivity as IDEs do.

> Honestly, I think I just... haven't ever felt the need to do these things in Java?

This is surprising for me, but hey, each of us are a different use case.

My recommendation is to try an IDE extensively, and then you decide what suits you better. I did this, and never looked back (for Java programming; I'm still using Vim extensively for general text edition, for example).