In this case, there is no proof yet. But, if in the Spring Game Buchner proves the best he should play first. We saw this with Book early on. He out-performed Wimbush plenty of times and was still relegated to #2 because of yet another Kelly infatuation.
I am a wait and see, but I'm just noting the evidence that does support that Kelly is very inconsistent here and historically has made pretty poor roster management decisions.
When there is proof let it roll regardless of age or tenure. The goal is to win and to win you have to have the most cohesive group of talented players on the field. Cohesive is the keyword and for the offense, that means creating the most first downs AND scoring the most points; with the fewest stalled drives. Much of this lies on the shoulders of the QB.
Rees for example was not the most talented but he was excellent in cohesion, moving the chains, and generally in leading the team to points.