Counter-perspective, but largely in agreement: I did grow up with a mobile phone and instant messaging and whatnot, and so using Slack (and to some extent, Zoom, as much as I dislike video compared to text) feels very natural to me.

To me, as someone who has deep and meaningful friendships with certain people mediated almost entirely through Discord messaging, which is basically non-work Slack, asynchronous mentorship and collaboration don't seem strange at all. I do recognize not everyone's a fan, and that there is a certain learning curve involved if you're not used to it (gamers, for example, seem to fall into virtual work naturally), but it's absolutely doable and these C-levels who say it's not are behind the curve.