He can get more out of players, but I think it's naive to think he can change them completely. Unless Jones being dross in that respect is due to the tactical instruction of various Kilmarnock managers, I'm sceptical Gerrard can get more out of him.
If it was Jamie Walker on loan with an option to buy or buying Jones, I'd take the former.
I do hope Murphy makes a full recovery from this injury though. Hate seeing injuries ruin it for players who genuinely want to do a job for us.