I have my computer configured so that most file types open in Sublime Text for that reason. For projects with a lot of TypeScript I'll open a project folder in VSCode, and then just leave it open indefinitely. Because that part is annoyingly slow, as you say.
I find it less annoying than Slack, though — seems to me that once VSCode is open and focused on what you want, it is a lot faster than Slack at all the basic operations (switching files/channels, searching, etc). Slack feels more like most other Electron apps I have tried — slow enough at just about every little thing to be constantly annoying.