I don't think di Montezemolo ever met Nuvolari, Ascari, Clark (they were all dead by the time he was hired by Ferrari) - and he certainly didn't "meet" Fangio, Moss and Stewart in their driving prime. Socially perhaps.
Di Montezemolo's time started in the mid 1970s/Lauda 'era' ... and he would have "met" Villeneuve who Enzo Ferrari himself said was "the greatest since Nuvolari".
[Bias? Probably. Ferrari 'fell out' with Ascari, Fangio and Lauda - all World Champions in his cars. And, Villeneuve was somewhat like 'a son' to him - and died in one of his cars.]
Anyway, after Gilles, came the likes of Senna, Schumacher/Hakkinen and the current crop.
Most historians who have seen it all rate Shumacher BEHIND the likes of Senna, Clark, Fangio...some even rate him behind Prost and Moss.
Push it forward, and it's hard to put Hamilton ahead of Schumacher - and Alonso did not beat Hamilton.
Perhaps Alonso is "better" than Schumacher - but two things are clear to me:
1. Alonso made a lot of mistakes in 2010. They - either individually (but most certainly collectively) - cost him the Championship; and
2. Over the first 5 Grands Prix of 2013 the Ferrari-Pirelli 'package' was superior to the RBR-Pirelli 'package' - yet it was Vettel who led the standings...and, then, at the next GP at Monaco, Alonso was simply terrible.
I really can't take di Montezemolo seriously. Part of it i'm sure is that he's talking to Spanish media and the other part is that old Italian is trying to make sure he does his part to keep Alonso motivated to fight for and stay at Ferrari in 2014, 2015.