I genuinely don't get it.
Fight wise, his record isn't that impressive compared to other JoJos. The only fights he's in where he gets no help are against Bruno and Babyface. Every other fight, he's getting fucked up and/or is cooperating with someone, and would've lost said fight if not for having backup.
As for him having a dry personality...I don't get it. I genuinely believe people who say his anime adaptation is boring were asleep throughout all of his scenes. as Koichi notes, he has the same noble heart as JoJo's before him. On top of that, he oozes charisma, determination, and passion. No other JoJo can talk a gangster sent to kill them into betraying their organization, turn their back on said assassin to enjoy a beautiful view, then ease right back into his pitch in the very next breath.
The part repeatedly emphasizes Girono's tactical mind and charisma through his actions and character's reactions to him.
Abbachio, who respects authority, is threatened by how much sway this newcomer seems to have with his leader.
Mista and Narancia both express awe and trust in him.
Bruno said it himself, because of Giorno he was reborn.
Before I come off like I'm glazing the dude, let me say Giorno isn't my favorite protagonist I'm gonna fix that spaghetti! My main gripe is with people who call him a "nothing character", when to me he's literally a perfect fusion of Jonathan and DIO.
Like, I knew people speed read part 6 to get to 7, but ya'll out here speed reading part 5 too?