Some QBs come out of college and immediately master the pro game, like Dan Marino. Others, like John Elway, did not look that great in his early years.
IIRC, Denver fans used to spit on Elway his rookie season, as he went into the locker room. Now, he could be roasting a baby on the steps of the capitol, and I highly doubt much would be said by the very same people.
Interesting comment on Dilfer. I live near and know Trent. In my opinion he excelled because of his football IQ. He did not have the skills the analysts treasure. All he did was win.