" Tsuna, you haven't changed much, but that's a good thing," said Reborn.
It was true he didn't change is some ways, but Tsuna actually changed a lot. He had a kind heart that weathered the hardships that came with becoming a mafia heir. He made friends, and he held onto them with his dying will. In the beginning, he had been passive and unsure of himself, but as the years went by, he became an outstanding leader, who took the initiative in protecting his friends.
If Tsuna had stayed withdrawn and afraid or cynical and ruthless, then one could say he didn't change at all, but he did change.
He was Reborn!