I really, really wish that Slack would learn this. Their constant creep in features means I lose about a cumulative hour every other week trying to do something that I once knew how to do.
Reminds me of Microsoft Office's latest big UI change, removing drop-down menus in favor of "toolbar ribbons". Went from being a power user / expert to a complete novice over night. I always wonder if there's a better way to make those types of transitions.
Something needed to be done though. I use LibreOffice every few weeks, they still use the toolbar UI by default, and it's faster to google where an option is than to go hunting for it.