If Sinner didn't have that bad of a track record in closing out matches, I probably would have dismissed it as a one-off. (And let's face it, if Sinner was a better closer, he'd probably have close to ten slams by now.)
But his history of not being able to close out matches is definitely relevant. Remember, Sinner was serving for the match at the French Open final last year... and he choked! It may be part of a bigger pattern.
Could you imagine Rafa ever choke a lead like this? What about Federer? Or even Djokovic?
None of the greats would ever blow a lead like this. Sinner does, and that's why he has only 4 slams, instead of like 8 or 9.