Considering their new desktop app didn't have even the most basic error handling for connection failures (during downtime people had bricked apps that displayed a white screen with a HTTP error), I have absolutely zero faith in Slack's engineering capabilities.

That's not an indictment of the engineers, but it's an indictment of the executives and managers responsible for the lazy stagnation they're currently in. The quality engineering is gone.

Headcount is way up, engineering budgets are way up, but feature velocity is non-existent. Meanwhile Teams is moving at lightspeed in comparison. While Teams might not be there yet, at least they're trying. Slack is doing nothing.