You don't need a running QB, you need a QB that can extend plays, when a play is shut down. Purdy can do that and to some degree, so can Darnold for example. 3rd and 6, nothing is there, the QB takes off and gets just enough for the first down.
That is what the Rams are looking for, Stafford does not have the ability to do that and IMO, the successor will. Mendoza for example can do that, obviously Moore can too. The goal is to find a QB that has that ability, pass first, but extend the play, when nothing is there and those QB's were always in vogue. Staubach, Bradshaw, Montana, Favre, Rodgers (younger), Elway (older) and even a younger Tom Brady, in fact, that is why they liked him over Bledsoe.