In more than one way Marchisio is what Juve needs as a captain later on. The fact that he is from Turin, the way he became a first team player, his attitude and above all having a captain in the middle of the pitch are all reasons to make him the better candidate.
Don't agree with any of your reasons.
That he's from Turin is cool from a PR angle (in that charming "boy leads hometown club to glory" kind of way), and also somewhat validates the youth setup, but other than that? Fairly inconsequential, considering 95% of our first team members aren't themselves from the neighbourhood and thusly it wouldn't resonate with them. I'm a believer that a captain leads on the pitch by example, with spirit and determination, and between the two? Chiellini wins this by a landslide. It's not even close. At all. Time and time again he's driven the team onward, single-handedly often, particularly when we most needed it. Marchisio? This is a guy who struggles to be relevant on the pitch much of the time ("Mr. Anonymous") and was himself supplanted by superior players in the center of the park.
As for the rest? How did he become a first team player? Calciopoli, mainly. The dearth of talent we had, the necessity for a "rebuilding from within" and all that. He never forced himself into the team on his own merits, but rather, took the opportunity presented him (more of a victor of circumstances, if you ask me).
His attitude? I'll give you that. He's professional. However, we have a number of players with that quality. What makes him more special than them in that respect?
As for his position on the pitch... Yeah, I guess it's nice to have a captain in the mix of everything when it's predicated upon him being charismatic, motivating and able to drag the rest of the team forward. The problem? Marchisio doesn't really embody any of that, in my opinion.