> If people cared, then all iOS apps would use standard styling, but the matter of fact is that every app has its own style, which does not stop at colors.
This assumes they have a choice between equivalent apps that OS-integrated and one that are not. Many times, they don't.
Anecdotally: while some people don't care about consistency in the art they put on their walls, most do.
Slack is included in the "apps that you use all the time" rule. Also in the "apps you don't have a choice about" rule.
(Edit for spelling and wording)