It depends on the semantics of "everyone" and "knows". The X11 selection bindings predate CUA clipboard usage by a few years, actually. But in any case, the contention was that they were simpler, not that they are standard. And they aren't.

You can cut/paste within your editor just fine. The subject at hand is window-system level clipboard/selection interaction, and in particular the presence of standard key bindings for them in various environments. While some terminal and editor apps do have keyboard bindings that interact with the OS clipboard, none are standard.

Basically, yeah: you had to use the mouse to select it in the first place. Using the mouse to paste it is easier, not harder.

Yeah, that slows down typing a lot. Luckily people on a laptop can use the touchpad which lies just below the space bar. I have a laptop with physical keys around the touchpad so I even have a button to paste. No need to tap, double tap, etc. I think that I never used a mouse in the last 20 years.

I can hit the middle click for my Trackpoint without leaving the keyboard :3