While I'm not sure this ruling is good, your argument is making it a bit too easy. Amazon does not naturally "provide better service" that others can't.
> free shipping for Prime customers
could be offered by sellers using other fulfillment too
> fast and reliable shippings
Not something only Amazon logistics are capable of
> easy returns
Not something only Amazon logistics are capable of (at least here in Germany, they just give you a label to put it in the normal postal system, as do most retailers)
> a networks of lockers so you don't have to wait for the package at home
That one is tricky. Although I guess the market dominance argument could still be used to say "well, your problem to figure out how to solve that, it's not absolutely impossible to let others ship stuff to those too"
For the first three, the pro-Amazon argument is of course that if third-parties do parts of it, Amazon has a hard time ensuring and monitoring quality of service, which is a problem for a "premium" product that's supposedly all about that - and which is popular because of a reputation to delivering on that, and it's unfairly harsh to go after that.
(The obvious fix of course would be for Amazon to not do fulfillment for third parties in Italy - if they are not in that market, they can't be accused of distorting it. If that'd be better overall for customers and sellers though? The theory behind the competition law says yes, at least short-term many might disagree)