FWIW my take on it is this:
Whilst SJM would not have been my first choice, it's hard to deny his work ethic. On his day he is excellent, but as others have pointed out, he is streaky.
Perhaps SG wants the work ethic to be at the heart of the team, and I can see why. Maybe not leading the team by example in terms of technical ability like Jack did, but perhaps more in terms of effort. It's difficult to know without being around him whether he is a leader, but I am giving SG some lattitude here, as Stevie was absolutely a leader of men on the field, and he therefore should know what that takes.
Plus, I remember when we gave Jack the captaincy it was kind of the making of him. He performed better, took more responsibility, and became the heart of the team. At the time Jack was probably the last person I would have selected, because of his lifestyle, but it worked out pretty well.
Maybe this will lead to more consistency from SJM, particularly as he will be able to operate further forward, and with fewer defensive responsibilities now we have Kamara.
I guess the jury is still out, but then I suppose it always is. We don't really know what cliques and groups exist within the squad. Maybe John is at the centre of the culture of the club.
Good Luck, big John. Hope you prove us all wrong and lead us to greatness.