Yes, you need upside to win games.
But, if you can't win all the gimmie games with that "more upside" alone, then there isn't in fact any upside. It's a distractive facade.
Buchner has not shown the ability to do that. Wimbush could not do that. Golson could not do that (paired with Rees as the savior, he was close). Yes, Book fell short of the upside and so will Pyne. Rees was the weakest of all three at upside, but all three where much greater on the whole and won more games than any of the upside QBs. Because the upside couldn't even when a majority of the games where they could just out-talent the other team.