Everyone gets that.
But he’s not why the offense sucks. Great passers make the players around them better. Dak isn’t there yet.
How many QB's in their second year have been there?
There are a multitude of reasons for the offensive struggles this year, many of which you already listed, but the overall lack of speed/explosiveness out of the WR's/TE's is right at the top of the list. When you combine Witten's age, Dez's decline, Beasley basically being a glorified TE who only operates within 10 yards of the LOS, and the coaching staff's inability to scheme easy throws for Dak you have a pretty major problem.
Getting away from the more systemic problems and focusing more on Dak, I think it's clear that he struggles with top defenses when the game is put on his shoulders. He can carry the team against average, maybe above average and worse defenses, but against top-tier defenses he struggles if the running game is shut down. That is where he will have to improve moving forward.
He basically carried the team at Arizona and against the Packers/Rams are home without much help from Elliott, as well as at the Giants. Elliott was poor to start the year and there wasn't much support from the running game in New York, and it was mostly Dak who carried the offense in all of those games. If the defense could've held their water for 2 minutes against Green Bay we'd be 3-1 in those games with the only loss coming to one of the hotter teams in the league.