I don't need efficiency. I need something that, given fuel, gives me power. And as someone who has donated to vim, was an early backer of neovim's bountysource, and loves his terminal: vim is my ion drive, IntelliJ and friends are my conventional rocket.
I've found it also works very well on Linux on a laptop with a i5-8250U and 16 GB of RAM.
The only thing that seems "slow" is starting up and indexing libraries and whatnot. Now I've never loaded the same projects in VSCode, but I'm not sure indexing would be that much faster and the startup doesn't really bother me, as I don't launch it multiple times a day.
I would not write Java anywhere but IntelliJ. Any long time IntelliJ+Java user has macros and templates written so that boilerplate is automatic. `psvm` is built-in, as is `sout`, but when I wrote a lot of Java I had ones for other common patterns at my workplace.
That said, given everything it provides I don't think there is a better tool for the job despite the performance issues.
It looks like maybe a macOS issue as Windows/Linux don't have the same problem, but there's a port of Java to Apple's proprietary Metal API in progress for some time. It's possible that will fix it.
The MBP i7 is terrible for this, and I get thermal throttling all the time when I use 4k external screens and anything remotely that seems like work.