I do think that with 4 majors already at (barely) age 21, Carlos is a real possibility to challenge the Big 3 in terms of lifetime Grand Slam wins. He's won more than any of them had won at this age, and he's already done it on all surfaces (it took Federer and Djokovic a long time to win majors on all 3 surfaces).
Sinner definitely has that potential as well, but it's way too early to discuss that for him — we can talk after he's won a few more. Actually, it's too early for Alcaraz too; we should wait until he's won at least 10 first, IMO.
I think Djoker will be out of the Top 10 by the end of next year.