This is the way I see it:
As many have mentioned, having 5 or more players in a leadership role is not a new concept and pretty much happens at every club.
A captain needs to be as close to the action as possible, where you can see those little details and hear what's being said. This is why I believe Fox wouldn't be suited as Captain.
RFM has been with the club for quite a while now, is a senior in the player group, knows the club's values, is well respected and probably other shit we don't see behind closed doors. It's a natural progression imo.
Burton is very early into his footy career, so giving him sole responsibility of captain, on top of being a playmaker and kicker, would be unfair. Mahoney is already halfway into his career, more experienced and could've easily been a captain for Parra. So having him alongside Burton is a wise choice.
So yeah I dont buy into this "but Mahoney hasn't even played for us yet" bullshit. He has all the attributes of an on-field leader. The rest is irrelevant.