I may give it another try... last time I looked at Brackets and Atom, they were just slow... which surprised me when VS-Code wasn't too bad.. may check atom again.. but still using sublime most of the time.
Try switching from autocomplete while typing to autocomplete via keyboard shortcut and it may already make a big difference - this helped in my case with the php autocomplete slowdown.
I'll probably give it another whirl, hopefully the React stuff will have sped it up a bit.