The idea Barnwell is putting forward is not "build a team around a good rookie QB" but "build a team around a long succession of rookie-deal QBs" by trading said rookie deal QB during/after the fourth year of their rookie deal. The idea being that you can trade said QB for another top pick, pick another QB, and continue the same process again and again.
The obvious question is whether or not a team can continuously draft good QBs who will produce in such a way that they can get those high value picks. Barnwell points out that with that trade you're not just getting another top QB prospect, but also the opportunity to put the money saved towards other key pieces of your team.