Basically, I want LibreOffice Calc to do what I tell it, not what it wants.
For example:
I understand your problem with pasting pure unformatted text. This may be more work than you like (we can try to automate that later) but when I paste data from Notepad, I am prompted with an import screen as you can see below. Select the column header(s) and then select Column type: Text. This should solve your paste/import problem. An alternative is to handle this with an AutoHotKey script.
Oh b.t.w. the @ is the format type for text, just like you have HH for 24 hour or ffffd for weekdays...
I had pasted numbers from another site and it kept coming up with dates. I just messed around and hit the arrow that's on the paste board to give me the option of unformatted text or HTML format. I selected unformatted, a window opened to show me the text I wanted so I pressed o.k.