Did you see the post he quoted when he said that? The discussion was about trading Brady, that's the context of his post. By citing the Herschel Walker trade, he's comparing the two situations, which, as explained before, is ridiculous, as they have absolutely nothing in common at all.
And no, my observation isn't irrelevant to your point. The fact is, the vast majority of the time, teams have a great deal of difficulty replacing their franchise QB. You listing the handful of occasions in which a great player at the position was immediately succeeded by another great is misleading. Yes, transitions at the quarterback position have to happen at some point. At the same time, the odds of you ending up with a John Elway/Brian Griese situation are much higher than finding yourself in a Joe Montana/Steve Young one. You think about moving on from Brady when signs of his decline are clear and evident for all to see. There's absolutely no way you can put a time limit on when you'll trade him/cut him or anything like that. Obviously, they have to start preparing a backup for when that time comes, but as long as he's playing at the level he is now, or even 85% or that, you keep him at quarterback, because odds are, you won't be getting the same type of production from his replacement.
