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.
Or who knows; could be something about the projects - number or sizes of files, language used and references between files, etc.