Long time slack app user here, I don’t know how you guys organize your slack but performance has never been an issue for our organization, I don’t think it would run any better then it currently does if it were an os native app, of course my machine isn’t a toaster.

It's not just the app being slower than the website, it's what it does to the rest of your machine.

Contained within a tab Slack can only use a set amount of resources allotted by the browser.

Whereas installing the app means it can go full hog.

One Chromium runtime managing five tabs is more efficient than five Chromium runtimes running one site each (because those instances aren't able to share anything with one another).