The "paste with styles" default is one of the worst things ever IMO. It's almost never what I want.
Still don't know of a single case where the "feature" was useful.
Paste with source formatting or theme, I can't recall the exact name right now, rules. It means being able to mooch slides from any file and use them with no real fuss.
An alternative is to turn the slide into a bitmap.
Your primary point is solid. Seconded.
Unfortunately it's rather easy to mistype it as ctrl shift c, which --as you might have guessed-- is "call everyone".