Something important must be different about our Slack environments. Maybe it's the number of users, or possibly the OS?

We're a small company (about 150 Slack users), and I've run the Slack (Electron) app on a 16GB M2 (macOS) and a 4GB Chromebook (running a non-ChromeOS Linux), and it has never had any noteworthy performance issues.

It still sucks, but not because of performance.