Slack has been a down hill project for the past 5 years and has become incredibly bad. Unfortunately,this should be the sentiment with all SaaS projects. When a platform, like in this case, is inherent to the value proposition and can not easily be exchanged (building programs around it), one should consider self hosting.
This is licensing problem, not hosting problem. VMware and Oracle didn't got it reputation out of thin air.
Organizations need to realize that being right does not matter if you are dead.