We have different circumstances right now. There's never been a bigger void between 2 players and the rest of the field. Ljubicic had more belief against Fed in 2006 than Zverev has against Sinner now.
Both Sinner and Alcaraz have all the data available from the big 3, they know what worked, what didn't, extra 20 years of knowledge/training/dieting/physio etc.
With new superstars you just never know until they pretty much start winning Slams or at least causing major upsets fairly consistently. But there are still voids, look - Djokovic had no younger ATG until Alcaraz came along in 2022/2023ish when Djokovic was already 35/36 years old and at the tail end of his big title winning form (and no, I don't believe he prevented Medvedev and Zverev from becoming ATGs, they just don't feel ATGs even if Djokovic wasn't there in 2018-2023). Someone can pop up even this year or it might take another 3 years. Now imagine 3 years of this era - that's roughly 42 big titles to share, 90-95% goes to either Alcaraz or Sinner - that single void puts both a tier higher and they will still be in or close to their primes at 26/28 with maybe even a decade of tennis left in both. Let's just wait and see and enjoy (or rather not) the moment.