Valve built more games than Epic in the past 10 years. Epic essentially only released Robo Recall and Fortnite + extra content, plus a spinoff of Rocket League which was an acquisition. Valve released a couple of duds (Artifact, Dota Underlords) but also some good games: Half-Life: Alyx, Counter-Strike 2, and Deadlock. They also did "The Lab" and "Aperture Desk Job" which, while not full games, were quite good as demos for their hardware.
I'm sure any studio would trade their entire decade of portfolio to get where Fortnite is. Sony did in fact basically do that to great failure (despite Hell divers 2 being very well received, it's no Fortnite).
