I think everyone agrees we need to develop Josh Allen to see what we have in him. The issue isn't whether to start him again, it's a matter of when! The original plan was to bring in AJ McCarron and have the kid learn for a year. That plan was dropped when AJ was jettisoned, Peterman fizzled and, in the absence of any other alternative, Allen started. This to rather predictable uneven results (for a rookie most have judged still very raw.)
Let's say JA is picked to start in two weeks against a tough Jaguars D and plays poorly. The hometown fans will be screaming for "Barkley" given his inaugural success. I don't believe that extra pressure will be good for the kid's development. (And he does need to develop: make quicker reads, stay longer in the pocket; improve his accuracy). Starting Barkley for another game or two, or until the veteran struggles, will benefit the kid in numerous ways. And allow the team, and offensive players in particular, to gain some momentum.