Ctrl+Insert / Shift+Insert should work consistently.

Right, so if a new Linux user who uses Ctrl+C/V in all GUI apps finds that he needs to paste something into terminal that should be perfectly obvious for them?

Or should that person feel confused and annoyed since they can't they don't know how to basic operation just so that "power users" could feel better about themselves (I can't think of any other reason which would someone think purposefully inconsistent UX is a good thing...)

Also "Insert" is not a thing on most laptop keyboards. So it would be Ctrl + Fn + Delete(or something like that) which is also perfectly obvious.

"Most" laptops actually do have an Insert key. Perhaps you've been using the wrong laptops? :)

Anyway, my comment was in jest. None of them are perfect, and to a non-Mac user, its imperfections make it "clunky", whereas they are used to imperfections of their go-to systems.

Bugginess one sees when switching to a Mac for the first time is really the same feeling for me like Linux feels to you.

I don't agree. This isn't about different behaviours in Linux vs Mac/Windows but rather about Linux apps having different shortcuts for common basic operations in different apps. That's just poor UX.

I think Ctrl-C behaving consistently in a Linux terminal, be it an actual terminal or a GUI-based one, is good behaviour. Ctrl-C for "copy" actually came a long time after Ctrl-C already had a meaning in a text terminal.

For that matter, how does Ctrl-C behave in Windows Command Prompt (if that's still how they call it)? In what way is it inconsistent: with the GUI or with the originating DOS terminal behaviour?

Mac went with Command and Control as separate keys on a keyboard, which avoids this particular issue, but it gets confusing quickly: what's a "command" and what's a "control"? Which key is to switch workspaces, and why is that "Control" and not "Command"? With every single shortcut, I wonder which was the one I need to use, and it's so hard to remember.

That's just poor UX.