I think the biggest thing to remember is that changing your build tool for a large project is going to be a massive effort, you're gonna need a LOT of hours to throw at it, and you might not find many benefits for a long time.

Starting a new project with it, so it can help you do things the "right way" is a much more attractive proposition.

That said, the IDE/tooling situation for Bazel was disappointing to me in the Java world too. It definitely lags and is incomplete.