I’d have him ranked as a high end backup. Here’s why.
He can win you games against easy teams. Teams with wins under .500. Anything above that and it’s a dice roll.
I also ranked him a backup because typically (unless you’re lucky like the eagles), you’re afraid about sending a backup to the playoffs. No other team in the league is more afraid about the potential performance about their QB in the playoffs more than the Cowboys. We have to worry about this every year, “will Dak live up to expectations?” The answer is always a big fat no. Do you think the Chiefs, Eagles, Bengals, Bills, Bucs, Dolphins, fear this issue? 49ers share a similar issue but they have a legit coaching staff, culture, tough attitude team that plays excellent old school football (good tough nose defense and great run game) that keeps them ahead of multiple teams.
Dak also takes up too much cap for his stats and eye test.
He gets a D+ from me overall. B+ against teams that are below .500. F for teams rated above .500. He also gets a knock grade because for some reason he sucks horrendously when playing in games with QBs named Rodgers and Brady. It’s almost likely he tries so hard to be “better” than them and he fails miserably every time.