Higuain is World Class! And that is not up for a debate. Whether he will make it in Italy or not is something that no one knows and can not know until he actually plays here.
That term world class is really misunderstood. There are very few of those players who have the rare qualities of intelligence, temperament and talent. Just the fact that you're wondering whether he will make it or not in another league shows that he doesn't bring a guarantee.
But would you feel that way about guys like Ibra, CR, Messi, Tevez, Aguero, Eto'o in his day, Drogba, Robben, Falcao, Iniesta, Buffon, Pirlo?
Back in the day, Zizou was what world class was about. Things are a little more diluted today, but still.
Personally, I think Higuain is a good player, with good mobility and a first touch. A continental quality forward, but is he the player you would buy at all costs, if you knew you had his first and most natural position covered by someone on 4.5m wages, and you would be spending big despite limited resources? Is he good enough to warrant that? I would be inclined to say no. Just my two cents.