Truth be told, there are no definitives here. Some great QBs started from day one. Some of those great QBs were successful early, some were not. Some great QBs sat a bit. Some of those great QBs were successful early some were not.
Some craptastic QBs started at once, some sat for a bit. They were in the end craptastic.
Starting early doesn’t mean a QB will be successful or not. Surrounding talent, coaching, division opponents, injury, karma...all play a part. Not all QBs with all the tools succeed. The reasons vary, but IMO have nothing to do with starting from day one.