I have a 2015 MacBook for work and use jet brains. It’s quite snappy and responsive. Id expect it to be better on newer hardware but am left wondering why performance degraded so much for people?
It didn't. Many people just want it to be instantaneous they way something like Vim or Sublime is, and it just isn't.
But it's in no way any worse on modern machines that what you see in your 2015 MacBook (I have several Macs and can attest). People complain despite getting better performance than what you get on later Macs/PCs.
The other case is too many / too slow plugins. Not all are made equal. But as far as the core functionality, there has been no regression all the years I'm using it.
I use IntelliJ on a 2015 Macbook pro and an equivalently old Dell Latitude running Ubuntu 20.04. The mac has only an i5 dual core processor with 8GB RAM while the Dell has an i7 quad core processor with 16 GB RAM. I hardly find any performance difference with IntelliJ on both the machines.
I too use it on an older (2014) mbp, and it is fine for Rubymine.
I highly suspect the performance problems some people experience are due to plugins. When I was doing some Elixir/Phoenix work, the Elixir plugin made it unusable sometimes. Clearly that plugin had some serious issues which would appear at times. I have not had the same performance problems in Rubymine or in vanilla IDEA.
I've had sluggishness on a 2019 MBP with totally vanilla Webstorm, no third-party plugins. It was usable, but bad enough to turn me off and send me back to VSCode.
My work laptop is a 2018 or 19 i5 13" MBP with an Intel GPU. It sometimes feels slower than my old MBP (i7 with Nvidia 680 or somesuch GPU). I doubt the CPU difference is the issue, but perhaps there's enough GPU difference that can cause IDEA to be slower on machines without a dedicated GPU.
Or who knows; could be something about the projects - number or sizes of files, language used and references between files, etc.
But it's in no way any worse on modern machines that what you see in your 2015 MacBook (I have several Macs and can attest). People complain despite getting better performance than what you get on later Macs/PCs.
The other case is too many / too slow plugins. Not all are made equal. But as far as the core functionality, there has been no regression all the years I'm using it.