I want the skipper to be certain of their place in the first team. Not sure our back row has candidates who are- there are so many great options to choose from.
It is a tough one, if you make Shields captain, and we go all the way to the Premiership final, two of Carr, Willis, Ashley and Young miss out on a starting slot unless Shields starts in the second row, and that is before we consider the incoming recruits. More importantly the players concerned would all know that. With Launch, all the other locks would know that too but they can't argue, if Joe is fit, he plays. Shields is miles away from that level of security currently.
Shields may also be away during the 6n if things go well for him, so whilst he may be a good candidate, better than Joe, for me he needs to establish that he is the first name on the back row team sheet.