There is a big difference though, being a stand in captain or a vice captain compared to being the captain of a club, arguably the 2nd biggest in the AFL and one of 60,000 starving members.
He's doing a stack of media and the pressure intensifies. He's also dealing with younger guys coming through and most likely mentoring them as well which is another burden.
Would be very few players who have been given the captaincy and have been dominant in their first year. There is a lot to adjust too.
All fair points but the reason he was made captain at such a young age was because of the way he played. His actions on the field personifies leadership so IMHO he doesn't/didn't need to change the way he played/plays.
I just think he is trying too hard to do all the things you speak of on the field when he doesn't need to. His natural ability and natural leadership ensures he does it, doesn't need to try to do it or increase the level of it
As for the off field stuff he has actually said he enjoys it so I don't think that has had much of an impact
As for other young captain of a similar age who have continued to dominate after ei made captain - Joel Selwood and before that Wayne Carey spring to mind. Selwood has not change the way he plays, the way plays is what leads his team mates