For so-called “important” collections, so far it has been both. Among the top U.S. collections that come onto the auction market, they have overwhelmingly been raw while still in the hands of the collectors. Frequently the submission for grading and slabbing is done by the auction house, as part of preparing the collection for sale, at GREATLY reduced rates from the “normal” prices. As time marches on, more material will arrive in the market already slabbed, but we’re faaaaaar from a majority in that status.
As for the world coin market, slabbed is still a tiny minority.