I'm sure Veron did have issues with adapting to the intensity and pace of the league and settling in England etc etc however what is often not given enough weight in these discussions is that as good and talented as he was - he simply wasn't as good as what we had already. Keane and Scholes were better players and whilst SAF experimented in trying to tweak the set up to accommodate him, as his time here progressed he became less worth the effort . I bet we couldn't believe our luck when Chelsea came in for him
My insight on him, since watching him his whole carreer and at times a bit hating him (mostly because of Bielsa (NT) and his stubborn self kind of fvcked up the Veron I liked) is that:
One of the main problems with Veron at United was that you already had a team with to the very least three "launchers of the ball": Scholes, Beckham and to some extent Keane. It's not that he "couldn't adapt to the intensity, etc", he came from Serie A where intensity, going for the second ball, presurring was at the order of the day, yet he never find his role and also Veron as great as he was, wasn't exactly Riquelme or Zidane regarding ball retention (neither were Keane, Becks or Shcoles). So at times when he tried to change his game to add more pause, to do such role he had moments were he ended being a tad out of tune or even reckless.
And waht is really more related to intensity, but not intrinsically because of the League per se, at that time Veron arrived to Man Utd he was already in the first pahse since his last season in Italy of what I call his "more lazy stage", he wasn't the 90's, dinamic "8" version of Estudiantes, Boca, his first stages in Italy and WC98.
He somehow bought the idea, hype of that superb 10 he never was, the hype was inmense at times (and quite deserved), yet that wasn't his real or more suitable role, less at that period of huis carreer. So from United, to Chelsea, to his days in Inter, that was a lot more passive and walking Veron, he at times in Italy played as a deep CM. Only when he returned to Argentina to Estudiantes he somehow (even old) had more solidarity, more intensity and for moments wiser game. His match against Barca for the Intercontinental and the way he carried Estudiantes to a Libertadores was his way to end his carreer on a high note.
I always thougth that Bielsa using him as his "10" while not using Roquelme or Aimar, also helped to him beilieving that he had that role in the pocket and for me, he was always a superb classic Argie number 8 like those from the 70's and 80's.