The iPhone took almost a decade to get to the appropriate functionality. The part you're leaving out is most executives just ended up carrying two devices and whined to IT about "why can't YOU make my iphone as good at email as my blackberry???"
>Enterprises thought they needed on-premise hosting of Exchange, Office and SharePoint instances under their control for email and productivity, until GSuite came up with a better, less configurable user
Except I can count on one hand the number of fortune 500 enterprises that moved to gsuite over o365.
>Slack is another proof point - the "consumerization of IT" trend in general.
I'm not even sure how this is relevant. Companies that were using skype for business or cisco jabber likely still have skype/jabber running alongside Slack.
This reads like someone who lives in the valley and thinks the valley is in any way reflective of corporate America. Hint: It's not.