It's valid because the great QBs, like those you mentioned, can overcome years of film on them. It's either because they don't have tendencies, they can alter those tendencies to avoid being exploited by a crafty D.
But it's minor because generally a good QB is going to... just... play good QB-- identify receivers, sidestep the rush, throw accurate safe passes, etc. And you don't need "tape" on that. I think "tape" is for players--especially QBs-- who are a flash in the pan and bust out after a few years. It's a more provocative argument than explaining it all away as regression to the mean. Will he tuck it and run with open receivers? When pressured from behind will he fail to sense it and step up? That sort of stuff is going to be noticed by good coordinators, hence the "tape" argument.
Tape is probably much more useful in exploiting offensive and defensive schemes than specific players.
