No, it wasn’t.
Just randomly looking at profootballreference.com … Manning, Favre, McNabb, Marino, Fouts, Elway, Ken Anderson, Esiason, Bradshaw, Greise, Bartkowski, Hadl, Starr, Tarkenton, Tittle all started at least one game as rookies and were full time starters by year two – Most were starting as rookies.
Mosat who didn’t start right away were either late-round surprises (Unitas, Montana), or bounced around other teams before starting, (Dawson, Layne). Usually, the only time you really see a talented young guy sitting behind a veteran is when the team is already winning behind the entrenched starter (Pennington behind Testaverde, Stabler behind Lamonica, Staubach behind Morton, Jurgensen behind Van Brocklin).
Oustide of that, you have to look long and hard to find examples of a team starting a mediocre veteran over a talented young guy for more than one season. Closest I can find is the Eagles letting Jaworski hold off Cunningham for too long.
So, I’m not at all convinced this was ever the norm. The platonic ideal, perhaps, but the reality seems to be that most of the time the young QB plays if/when he’s better than the old guy ahead of him.
If you want to say that the issue is the success of this year’s rookies, you have to define “success.”
Newton is the 15th-rated passer, Dalton is 24th, Gabbert is 30th. They are a combined 4-9 as starters. They’ve all refrained from being Ryan Leaf, but it’s not like they’re tearing the league up. Their numbers are somewhat inflated because league-wide passing stats are inflated, but two of the three are among the very worst starters in the league, and while Newton has huge yardage numbers, he’s thrown a ton of passes to do it, and his completion % is mediocre. Let’s hold off on anointing him just yet.
You won’t find many examples of rookies tearing the league up – including this year’s guys. But a list of guys who came in and played about league-average as true rookies would include Tarkenton, Kosar, Greise … as well as Chris Chandler, Jeff George, Jake Plummer, Charlie Batch, and Don Majkowski (and, of course, more if you keep looking). They’re not the norm, but they’re not all that hard to find. If you just looked for guys who played OK through 5 games, I’m sure the list would be longer.