There are levels to these things and Real Madrid has proven again that they are a classy team. I remember back then, Rashford has said in several occasions that Ronaldo is the best player but after he signed for Barcelona, immediately, he proclaimed Messi the best which brought back the old argument that Barcelona forces it players to say that their own is the best. Mastantuono press conference was few days ago and he proclaimed that Messi was the best player for him and their was no fuss or anything from Real Madrid. Class is indeed permanent.
The case of Rashford and Mastantuono is very different, he (Rashford) is English and he once played with Ronaldo at MU, it is natural that at that time he said Ronaldo was the best player, but after he came to Barcelona of course he had to change his view because he was playing for a club that had an endless feud with Real Madrid.
Meanwhile, Mastantuono, it is natural for him to say that Messi is the best player because he comes from the same country as Messi, Real Madrid also does not have a problem with it because Messi has a special place in the hearts of the Argentine people. If Mastantuono were from another country, Real Madrid would probably be furious with his statement at the press conference.
It just seems you're contradicting yourself, you said Rashford and Ronaldo once played and that made him to chose Ronaldo now that he is at Barcelona he has to change his mind. Mastantuono plays with Messi with the National team and he picked Messi but Real Madrid doesn't have any issues with that. Since both clubs had a feud with each other while is Real Madrid allowing it and Barcelona can't? That's class if you ask me. Real Madrid is a classy club alongside their fans that's why there's no problem. I still remember when Garnacho said Ronaldo was the best and he didn't play for Argentina national team that period.