If they don’t play before you have to extend them, then you lose that entire advantage and reason to draft a rookie QB (you also may not know if you should extend them).

2) because the premise of your post is wrong. Casual fans think that Rodgers and Mahomes were great because they sat, but the reality is they are great in spite of sitting. The only way to get better is to play. QBs don’t fault because they played game 1, they fault because they suck anyway.