But are people actually cutting their Netflix subscriptions because they play so much fortnite? I get that the game has a widely varied demographic, but I would assume that a majority of people putting in large amounts of "Consumer Screen Time" are probably still dependents of their parents, who likely maintain a household media streaming subscription of some kind.

I can't imagine that instances of people cutting out media streaming entirely in favor of gaming are significant enough to pose the kind of threat that Netflix is stating. If so, HBO and Hulu and all the others are in similar peril and the entire entertainment economy is due for unprecedented upheaval.