Age, leadership, respect amongst peers, consistency?
All the other half decent options are 30+. No point Cotch stepping down just to choose someone who is also near retirement.
The other option I like is Nank but he doesn't tick the durability box. He is in the rehab group far too much to be captain.
86 games from five years is hardly injury prone. That is 86 out of max 125 games with this year contributing to the games missed.
But its the future injuries that matter. How many of those injuries are ones from a weakness in body where you can expect reoccurrance.
Hate to see the load that he is prepared to take on work against him if captaincy is his calling.