Final score is a product of the entire Cowboys offense, the entire Cowboys defense, and the opposing team. There's so many moving parts beyond the quarterback... in fact, you've pretty much introduced every moving part possible.
If you want to talk individual metrics about Dak, like DVOA, PFF grade, QBR, or EPA, I'll play ball. But ranking a QB by their entire team's point differential is idiocy. If you're claiming that's the case, you're also claiming that Brock Purdy is a better quarterback than Mahomes, and I'll leave it at that.