I completely agree but the consideration is your phone is dead and you need to get ahold of someone. You should be able to easily memorize some way to contact emergency contacts IMO.
He's likely an llc taxed as an S-Corp. You don't pay taxes out of your business, profits after write offs are added to your return with a K1. You're likely thinking of a C-Corp.
I use Teams with one of my customers and Slack for most of my customers. I personally prefer Slack but Teams seems to get better day by day. Teams has threads down better than slack which can make it more advantageous. I think slack is better when it comes to being involved in different projects with different customers. I also prefer the ease of onboarding people to slack.
Please elaborate on "questionable corporate behavior". Everything else you said is matter of opinion and slack's growth would speak to the exact opposite.
"no encryption" - There is encryption, not end to end but data is encrypted at rest: https://slack.com/security
"horrible clients" - I disagree. They're not perfect but they work and are consistent 99.999% of the time.
"mistreatment of irc users" - People need to get over this. It's not IRC. That's like being upset that email doesn't support fax well enough.
While the encryption keys would be at amazon the slack data would be on "slack's servers" (AWS or elsewhere) meaning that both slack and AWS location of the keys would have to be compromised and then somehow associated to each other.
The problem is the average person doesn't have the money to pay a lawyer to fight off a company - especially the ones with teams of lawyers who need something to do.
This may be irrelevant but I'm curious why he chose a picture of himself to be at the top of his article? Seems completely irrelevant to the story but makes me wonder about him.