Even so, the "sort lines" example works well with even the out-of-the-box completion. But, Emacs sometimes has its own language for things. If I didn't know the keyboard commands for "make region uppercase" and "make region lowercase" (which in fact I'd forgotten, although they're pretty trivial), then as far as I could tell the best way I could find them would be: Google. Inside Emacs, I could type "M-x up" and get the correct "upcase-region", but if I'd typed "M-x upp", I'd be out of luck. And Emacs-ese for "lowercase" is "downcase"; I wouldn't have guessed that at all!
So I'm not sure the flow looks nigh identical for that many cases like this. The way I remember learning Emacs basics many years ago was actually through menus. Looking at Emacs's menus now, in v27.2, they're...kind of eclectic? The basics are there, but a lot, well, isn't. BBEdit is admittedly somewhat at the other extreme, with possibly just too damn much in its menus, but that does make a lot of its functionality very easily discoverable.
At any rate, I should be clear that I think this is a mild knock against Emacs; I bounce off it in part because of this relative lack of discoverability, and also because it just seems like it takes a lot of effort relative to most other editors to set up comfortably. The flip side of that is that, as the "Lock-In Effect" article notes, once you do have it set up the way you like it, you are probably never going to have any motivation to switch. That is absolutely not a knock -- it's configurable and extensible in a way nothing else is.