Both sides go over the top to irritate competing perspectives. The bottom line is that the current QB will not get much if any better than he currently is. He has shown and proven his capacity with different coaches and players. Beat tier 3 teams, split against tier 2 teams, lose to tier 1 teams. Extending him (which they will)-will extend the aforementioned results. If his best stats translated in the playoff games (consistently throughout the game)-everyone would be onboard with an extension.
Witnessing early success of young/inexperienced QB’s such as Mahomes, Burrow, CJ Stroud, Purdy, Lamar Jackson, Josh Allen should make you realize that success within 1-2 years of being in the league is not out of reach even if you are not drafting in the top 5 picks. Journeyman like Geno Smith, Baker Mayfield, and Derek Carr show you that teams can get immediate mediocre results after their starter leaves.
If you can blame getting into the playoffs only on the QB, can you see the hypocrisy of not blaming the QB for a playoff loss? Use a mirror when making an argument.
If you want the name (how about Russell Wilson?) of a QB that will give the team the exact or better production from the position immediately-you are wanting to go until the doors fall off. No team can exactly predict when a player will drastically fall off their previous production-but they can view trends and make decisions based on them. In my opinion, a QB should only be extended after 6 years (starting) if they reach a conference final or better. Dak has plateaued in a performance area that seems like a small difference but is unfortunately an extremely large gap with his surrounding talent.
The funny part is that the line of reasoning (name the next starting QB then) is inevitable (be it next season or 5-10 seasons from now). No one will be able to give a definitive answer then either-which is no reason to keep an incumbent starter that is only as good as his surrounding cast.