Ok so not all of the guys I'm about to list became superstars, but most NFL QBs don't anyway. There's a long history of guys who have sat a season or two before taking over or have bounced around a bit before becoming a starter.
You can say NFL QBs don't develop, but there's a lot of data saying otherwise. I do agree with the idea that some guys have it in them to become a starter and some just don't, but there are plenty of guys who weren't ready as rookies or were served well to sit and adjust for a 1,2, or 3 seasons. Also guys who started off rough before eventually becoming decent/average starters (like Alex Smith, who was a disaster early on in his career).
Here's a list i threw together in about 15 minutes:
Guys who sat before being ready to be NFL starters:
Aaron's Rodgers (needed those years sitting to work on mechanics)
Matt Hasselbeck
Tyrod Taylor
Tom Brady (though it wasn't just one season)
Phillip Rivers (behind Brees two easons)
Tony Romo
Steve McNair
Steve Young
Colin Kaepernick (though he only has had middling success...he wasn't ready as a rookie and eventually became a starter in a super bowl)
Trent Dilfer
Elvis Grback
Rich Gannon (super bowl MVP)
Carson Palmer
QBs who bounced around or took multiple seasons to become NFL starter quality (not a backup who happened to start games):
Kirk Cousins
Alex Smith
Kurt Warner (he was a practice squad guy who played in Europe before becoming an NFL starter)
Ryan Fitzpatrick (though he's more of a journeyman than a starter)
David Garrard (middling career, but got better after a few seasons)