The main problem with the slack client is not optimization of the javascript. The main problem is boatloads of pointless functionality that can’t be disabled.
When the slack client encounters a network hiccup, it re-downloads every image posted in every channel. How this ever shipped I have no idea. The client is essentially worthless on any kind of slower link, let alone the amount of ram that gets used by these downloads (they’re not intelligently stored on disk and composited on demand — if they were, the client probably wouldn’t re-download them). This occurs even if the user has said they don’t want images displayed by default (the client disobeys this setting on network hiccup).
Spending engineering time on animated emoji reactions and google docs display inline when the client can’t even reliably perform text chat functions is a misallocation of resources. You’re just incurring debt you’ll never pay down by marrying the entire design to a conceptual web canvas.