Agree. Facebook might still have them in some log or neural thinggy about you, but it will protect you from direct profiling like the Cambridge Analitica debacle. If it would turn out that deleting the activity still allows Facebook to keep them and sell them to 3rd parties, it would be a company-ending event, so there is at least self-preservation.
Why do you presume that once you come off facebook, your data is not used? That is not true, the data gets used and pimped around to the highest bidder. What is true, is that as time passes that data has less value (assuming you actually stopped pumping in the data in fb).
