Honestly, I think it's totally delusional to think that a QB like Dak will guarantee you win 9-12 games a year no matter what kind of talent you surround him with. There are only ever 2-3 QBs at the very most who you can be confident in them winning that many games even if they are surrounded by mediocre talent. Those top 2-3 guys are honestly the only guys that you should even consider spending even close to 15% of your total cap on (the stats suggest spending that much even on those absolute top level guys will rarely see you achieve any sort of success).
People might take that as an insult to Dak but you just need to look at how many 7 or 8 win seasons Drew Brees had while he was in his peak to know that there's no guarantee the Cowboys will have a winning record with Dak. Even if you think Dak is just as good as peak Brees was then you have to admit that Cowboys could easily have a losing season with Dak if the talent around him isn't right. From that generation only absolute peak Brady, Manning or Rodgers were capable of dragging an average roster to 10 wins.
To me, I feel like the absolute floor with a QB like Dak is probably around 5 wins a season which is actually a lot better than the floor for most QBs in the league. It is possible that I'm totally underestimating Dak and he is capable of dragging a weak team to a winning record. Unfortunately, though, we still haven't seen Dak have to perform with minimal talent around him so it's hard to judge just how much he can actually carry a poor team. At the time I thought we caught a major break when we suffered a horrendous amount of injuries in 2020 during the year our QB went down which meant we got a good draft pick and got our injury bad luck out of the way all at once. In hindsight, though, it would've been good to see how Dak performed that year with essentially just a bunch of backups. From what I've seen I don't think he would've carried us far but if he actually did take us to the playoffs that year I could perhaps understand giving him a massive contract. Shame we didn't get to see how he could perform without all that talent around him