I'm starting to think that Stefanos Tsitsipas has something to prove - that he belongs in the same breath as Medvedev and Zverev, which isn't so clear. Not only has he won far fewer big titles (2 to DM's 6 and AZ's 7), but he's fared far worse in ATP finals:
Tsitsipas 7-10
Medvedev 13-8
Zverev 17-10
With hungry younger guys on the rise--Sinner, Alcaraz, even FAA--and a solid group of second tier guys--Rublev, Hurkacz, Berretini, maybe Ruud--Tsitsipas may be in danger of being pushed out of being a perennial top 5 guy, if he doesn't take a step forward.