It is also very possible that Jodar and Fonseca turn out to be "lesser greats" like Courier, or even excellent 1-3 Slam types. We tend to (overly) focus on greats, and consider young players as failures if they don't--at the least--become Becker or Edberg. But really, tennis history also includes lots of guys who are lesser or near greats, and they're fun to have around.
During the Big Four era, four players dominated the big events with only a handful of other guys winning big titles. The last decade or so has seen us gradually shift back into a context in which a lot of guys win big titles. But it doesn't have to be Sincaraz (tons) or Rublev/Hurkacz/Fritz (1-2). Medvedev and Zverev have somewhat split the difference, but chances are both (or at least Meddy) will stick to one Slam. Who knows, maybe Jodar and Fonzie will end up as 2-4 Slam guys...no shame in that. I mean, even if Sincaraz somehow manage to win 20+ each, that's one fewer 20-Slam winner to bogart all the trophies, so more to go around.