You can make a strong argument for that. Fouts got a lot of credit for his 4,000-yard passing seasons. But he wasn't the first to do it. That was Joe Namath, who only managed it one time in his career. Fouts improved on that, but still only did it 3 times. Then along came Dan Marino, who you could also make a strong argument for. He had 6 seaons with over 4,000 yards passing. Throw Warren Moon, John Elway and Steve Young into the argument. They all did it, too.
But before Peyton came along, a 4,000 yard passing season was something of a rarity. It was a career-defining accomplishment. Only 13 other QBs, before Peyton, had EVER thrown for more than 4,000 yards -- most of them only once in their careers. And a lot of pantheon QBs never did it, including Joe Montana and Terry Bradshaw. They each played on the greatest teams of their respective eras, but that doesn't make either of them the best QB of all-time, despite what a lot of people seem to think. Joe Theismann won a Super Bowl. Jeff Hostetler won two. Best QB of all-time? Nobody would ever say that. Think about that when you consider that Peyton Manning AVERAGED more than 4,000 yards passing per season over the course of his entire career.
4,000 yard passing seasons are a lot more commonplace nowadays. The game is different now. And that's because of Peyton. Brees has done it 12 times. Brady 10. Peyton's career was shorter than both of theirs and he did it 14 times. Put that together with his high career passer rating, NFL records (including most league MVPs) and being the ONLY QB in the history of the game to lead two different teams to SB wins.