Agree with what you are saying broadly but its all if's but's and maybe's if Benitez was still here. There is a very good chance that irrespective of whomever was manager the nosedive in form Oct - Jan might have been too steep to recover from.
We absolutely have average players, some not even that and their ability and ego are not aligned. Think in Digne's case he was good enough but wasn't prepared to sacrifice for the team, but maybe not so easy to sacrifice when the results don't match the intention. A pity how it played out really because we would have been better off with him in the team over the last couple of months.