The best rookie QB prospects are usually drafted (often at #1) by the very teams that need to build the rest of the team (including the coaching staff, but in this context, the O-line, WRs, RBs, TEs) and hire some older talent (which is what the Browns and Jets are doing, and soon, so too the Steelers) to run the offense. Instead, promising rookies never learn how to play in the NFL because they’re either running for their lives or flat on their backs a lot. Their careers are over before they begin.
You rebuild by going after the trench players. If you have a good offensive line, regardless of the rest of the personnel, you should win at least 6-7 games.