You may think he's been around awhile, but he's just 22. I don't even think it will take him as long as it did Stan to figure out how to win big. Even Cilic won a Slam, and that in the era of the Big 3-4. And that era is ending, either sooner or later, but, as I mentioned, Denis has the time to wait them out.
Actually he made his big splash back in Canada Masters in 2017, which is 4 years ago.
Not to be the voice of pessimism, and I wish Dennis well, but it's hard to tell at this point in his career if this is his highwater mark or the start of getting to the next stratosphere level. "Just 22" isn't what it used to be. Certainly he's talented and has power, but the question with him is can he reign in his worst tendencies.
My bigger point is I'm not so sure he can "wait out" Medvedev, Tsitsipas, Zverev, Rublev, Berretinini, etc who are also at the cusp, i.e. will Theim also make a comeback? and we are not even talking about the younguns nipping at his heels such as his compatriot Felix AA, Jannik Sinner , and dark horses such as Aslan Karatsev, Karen K, Casper Ruud, etc plus the promising rookies ala Sebastian Korda, Musetti, Carlos Alcaraz, etc.
IMO it's a fairly large pool of contenders once the Big 3 are gone, and I'm not betting on all of them winning Majors in their careers. There could be another 15 /16 year old wannabee GOAT lurking even as we speak.
OK, Maybe I am the voice of pessimism.