Personally the Slack UI is very not "natural" for me, both before the redesign and after with new desktop UI. The iOS app feels better in the new version, but also something is very not consistent with my experience with other apps.
In the desktop case, for some actions (like leave a channel), I have to click on every element which looks like it clicking it would open a menu, until I find the right menu with that option.
On mobile, I find it very difficult to navigate quickly between channels/DMs, and always have a hard time when trying to open a "DM with several people session". Both a new one, and finding one I know exists in my history.
