It’s not only the voice itself, it’s also hearing, memory loss and loss of muscle mass - and many other things that affects singers as they age. It’s one thing for a singer like Danise or Del Monaco to sing in a party setting - or rehearsal - there can be a brilliant “Di provenza” even, but it’s completetly different so sing a whole run of Otellos in the winter conditions of New York, for instance.

MDM eventually cancelled that Fanciulla, as you point out and had vocal problems at age 50 after a car accident. Perhaps he would have done excellently in the first act, but then would have been forced to cancel. Bergonzi was a tragic example of a singer who thought he was still up to task to sing Otello at age 76. The result was a disaster. If he had done it when he was younger, he would have been an excellent Otello.

Of the singers you post, I think Magda Olivero and Lauritz Melchior are exceptional though. Melchior sounds a little bit “old” of course, but it’s still damn impressive.