Oh, the original comment was about the WebKit wrapper. Well, that this is using as much memory isn't very surprising. Why would Slack use less memory in a WKWebView than in an Electron frame? It is essentially the same app (with the Electron app providing a set of extra platform integration benefits).
Any performance differences between the two approaches should essentially boil down to the Chrome vs Safari differences.
Any performance differences between the two approaches should essentially boil down to the Chrome vs Safari differences.