First year as a starter is a separate category. I do recall recall Mahomes went for 50 TD's and 5,000 yards his first year as a starter and came up short in the Offsides game. (That's back when Tom Brady got all the calls lol.)
Yeah, I would put Kurt's first year over it. Mahomes changed the position and the way defenses play him.
The GSOT changed the game. The GSOT is known as the godfather of modern NFL offense and Marshall Faulk is still the greatest all purpose back ever. Nobody was all around better.
Jayden Daniel's season isn't even close to Mahomes or Warner's first season. That's why it's strictly the best season for a rookie QB, a much lower bar.
Shoot, I remember Sam Bradford had a record setting rookie year. The bar has been raised a lot.