This Dak video is okay, but it is disingenuous. The reviewer cherry picks Dak's worst games in the second half of last season to create his video. You don't grade a quarterback by looking at a lowlight video; if you looked at a 2016 highlight video of Dak you would form completely the opposite conclusion. Dak played poorly in the second half of last season, which this video covers, but was good the prior 24 games. In my opinion there were a couple of reasons why Dak played worse in 2017 than he did in 2016.
First of all, the O-Line was worse. In the first half of the season, La'el Collins had some protection issues, and faced many of the league's best pass rushers but the O-line was generally still good when Tyron was in. In the second half of the season, Tyron missed some time, Dak was hammered in the passing game, and his mechanics broke down.
Secondly, a couple of things happened after the Zeke suspension. Dak appeared to press more, which lead to an increase in bad decisions. Also, the Cowboys stopped running play action, I think they ran 12 play action passes in the three losses to the Falcons, Eagles, and Chargers. This was partly due to pass protection issues, I would guess. The Cowboys need to run play-action passes to be successful with Dak as QB, that is his #1 strength as a passer.
Dak has his limitations as a QB. He doesn't always go through his reads quickly enough, which can cause him to be late of throws. He doesn't throw to the deep middle of the field, and he can't throw the fade properly. He will sometimes check down when there is a guy open downfield. He is not the best guy at throwing receivers open. He was also the best rookie I have ever seen at not getting baited into bad throws, he can be very accurate in the right circumstances, he is a good leader, and he can be great in the red zone. He can still get better.
So with all of that being said, I think if Tyron is healthy next year, and Collins stays it RT, and Zeke plays 16 games, Dak will bounce back. The reason I think so is that Dak had all of these problems at Miss St. in his final year too, and bounced back in his rookie season with Dallas. His mechanics broke down under severe pressure at Miss St. too, he was one of the worst draftable QB's at throwing at covered receivers (but the one of the best at throwing to receivers with separation), and he was inconsistent with his accuracy then too because his mechanics broke down.
Dak is a good but limited quarterback. If you protect him and don't let him consistently get hit, and incorporate both a spread offense and a lot of play action, he will not make mistakes, and he will make enough plays for you to win. I expect that as long as he is Dallas's quarterback, the Cowboys will spend a lot of resources on the O-Line, and will start drafting smaller, quicker, and faster WRs, in an attempt to avoid the problems they had last year. As a Cowboy's fan, I would worry more about Tyron's back than Dak's play at QB.