Same exact experience here. Like, I could never get ES6 highlighting to work in Vim. Just flat out didn't work, so all non-ES5 code I write looks terrible. Could be a conflict with my theme or something else. I don't know, or care to do the work to figure it out.

I used Vim for a good 5 years. I still miss many things about it, but a shitty default UX is not one of them.