Slack is eventually going to write native apps once they realize that productivity software shouldn't be developed like an ad product from Google. It will take Teams winning because it gets included in the Office 365 subscription for several quarters before they come to the realization that they need to compete on user experience.
I mean, I agree, losing mass marketshare SHOULD lead to a major shakeup on trajectory, and competing on desktop user experience would be a logical next step. But... back to the first sentence of this comment.