I tried using rubymine for a bit as well, but I could never get it to not be slow as hell (I'm on a 2015 mbp with 16gb of ram). Tried tuning the settings a bit, turned on the fast typing config thing, still really laggy.
The one thing I was thinking was that I was also developing in a docker setup, so maybe file access was interfering or something? I haven't run a test outside of docker, so can't really verify and have moved past rubymine for now.
I do also some python and js, is quite amazing :)