It's going to change over time
Tier 1 2020-2023: Medvedev, Thiem, Zverev, and Tsitsipas in some order in the top 5
Tier 2 2020-2023: Rublev, Shapovalov, Auger-Aliassime in the top 10
Tier 3 2020-2023: Coric, De Minaur, Khachanov, Opelka, Fritz in the top 20
Tier 1 2023-2026: Auger-Aliassime, Tsitsipas, Zverev, Sinner in the top 5
Tier 2 2023-2026: Medvedev, Thiem, Rublev, Shapovalov, Alcaraz in the top 10
Tier 3 2023-2026: De Minaur, Coric, Khachanov, Opelka, Fritz in the top 20
Some Lost Gen guys will stick around and fill in some of the other spots, or perhaps a newer youth movement behind FAA/Sinner/Alcaraz