Interesting. So you're saying that it really 'spins the fans' when you run slack as a pure web app as well? It seems quite lightweight to me, on latest chrome in Ubuntu on a late 2016 macbook pro.
I guess it's too early for me to evaluate the performance of Twist, because I am not on any large teams there. But I can see that Slack at least, has room for improvement in rendering performance. Perhaps there is some general optimization they are missing out on, like immutable state + shouldComponentUpdate. That one saved a flailing app of mine in the past.
I'm in Firefox on Linux, i7-4500U, 8GB ram.