Well, Nole is arguably even more dangerous on hard. So he will be one of potential winners in New York.
I don't think Alcaraz will be dominating ATP alone. I believe some serious contenders will appear sooner rather than later (just like Rafa showed up when Roger was dominating for several years already).
You might be right and it is not that I am too pessimistic about the future competition in tennis, but it's just that for the moment the idea is quite real if nobody shows up in the next three years or so that Alcaraz might be dominating the sport for a long time. The US Open will be the next major milestone for Alcaraz because beating Nole on grass was big, but beating him on the hard court as well could also make Nole suffer a lot mentally because he was aiming for a few more Grand Slam titles, but Alcaraz could turn into the opponent that Nole for every other player for so long, the bogey opponent.