Forgive me for repeating myself.
A long time ago, high school and college teams didn't throw the ball. It was option stuff, T formations and running backs play after play. As a result, once you got to the pros, there were only a handful of guys in the world that were big enough, smart enough and had the throwing ability to be NFL quarterbacks. A lot of teams were starting QB's who had no business being there. Lynn Dickey, Mike Pagel, David Archer, etc. etc.
That isn't the case anymore. Beyond that, baseball isn't as popular or you get people playing both sports so you get more big guys that can throw starting pretty early. Positional scarcity isn't what it once was at the QB position. A lot of the starting QB's from the 80's couldn't make a roster if they played today.
What determines how well a QB does nowadays is his line, his receivers and his coach. There are a LOT of guys that can throw the ball nowadays and if you put them in a good situation, they will look good.
Dak is better than Dalton but if you can keep Dalton for $10m per year, you could buy multiple high level players for the difference between the two. The TEAM would be better with a competent QB making $10m vs an above average on making $35m.
Personally, I wouldn't give Dak what he wants. Let him play on the tag this year and see how both him and Dalton do in practice. Play the best guy this year but then go with the best value next year. If that's Dalton, tag and trade Dak.
And yes, Dallas paid Romo. How did that work out for the Cowboys?