I don't think there's any chance Davies will ever reach the performance levels Rose reached in his prime. Davies is a steady but unspectacular full back that will give you 6 or 7 out of 10 performances (last season he didnt even do that tbh)and as a back up I trust him but not as a starter.Davies was struggling with a groin injury for most of last season, clearly he is the one Poch actually trusts for the future because he just signed him to a new contract. He's generally been very reliable which is the opposite of Rose. You never know what you are going to get with Danny and we can't keep relying on players like that, not when they are supposed to be senior members of the squad.
If Rose goes we definitely need to bring a left back in.