Those players are pretty good players! Here are their rankings at the time they beat Nadal:
Alcaraz: 9; Shapovalov: 16; Zverev: 6; Rublev: 8; Djokovic: 1; Schwartzman: 15; Tsitsipas: 9; Thiem: 5; Fognini: 18.
So, they are all top 20 players, and of the three outside the top 10, two of them are best on clay and would probably have been ranked higher than they were with a clay-specific ranking. Sure, I was exaggerating in my previous post, but even with a weaker than ever Nadal, I think he can lose to quite a few players but is likely to win against most. Not being seeded will mean he can face tough players early, true.
At Roland Garros, he did win three of those four years and his only loss was to Djokovic. So, at least in Bo5, it's still an open question whether anyone bar Djokovic can stop him, and Djokovic himself is struggling lately and had a 1-2 record against Nadal at RG in the years in question.