Do you think all young players are not "the real deal" until they either beat Nadal/Djokovic or win a Slam?
It's harsh, but essentially. The Big 3 era is just so odd. Generations used to overlap, bleed into each other in terms both generations playing championship level tennis at the same time (e.g., Agassi, Courier, Sampras winning Slams while Becker,Lendl, Edberg were still winning Slams), or at least the younger generation announcing themselves before winning a Slam and the other generation retiring - e.g., Fed beating Sampras at Wimbledon in 2001, Sampras going on to win a Slam after that (showing he was still champion caliber when Fed beat him), and then Fed winning his first Slam in 2003 after Sampras had retired. Players have almost always served notice of potential ATG status in these ways.
Again, if we're just surmising that they're going to be "great" players and have very successful careers, maybe including a Slam or two (or maybe not), then it's probably already fair to say they are "the real deal." But, in the context people are talking about Sinner and Alcaraz - they're going to win 5, 6, 8 or "double digit" Slams and become ATGs, then yeah, I expect more to pronounce them the "real deal."
