What happens if when they have to face real competition, they are an abject failure?
That's not even a question to debate, since you have provided a scenario that leads to only the answer you want to hear.
Here, let me do that for YOU:
"What if we keep Martinez at starter, but he refuses to run and his passing mechanics regress to throwing off his back foot again while dropping his shoulder, and he starts locking onto receivers again while losing his cool in the pocket and refuses to pitch the ball to the I-back on options until they are pinned up against the sideline and he starts fumbling twice as much as he does now? Are you willing to keep Martinez as quarterback over the other two even if he singelhandedly loses EVERY game left in the season?