The runtime performance lost using ES6 features is minuscule compared to the runtime performance lost by using Node.js in the first place. If the difference in performance for the ES6 features actually matters then you have made a grave mistake using Node in the first place.
Are you comparing node to C or Go or something else?
It's funny, my big a-ha moment on performance happened when I was working at a bank and could only code in vba (i.e. excel). All of a sudden -- even on small data sets -- O(n^2) was unacceptable and I needed to think about algorithms to get to O(nlgn).