He has grown into his role, and as Ralph stated " I like him, he talks" which sort of indicates his leadership credentials on the pitch.
Yes he is prone to a mistake, but he is certainly no more prone to these than many Prem CB's - Think Stones, Keane, Otamendi, Lindelöf, David Luiz, Mustafi, Lovren and many others... All of which make far more balls ups than Jack.
He's doing a really good job right now.