And on the point of Canada, he has literally never made a good offense in either college or the NFL as an OC. Just look at his resume and how his teams ranked in points/game in his college career:
2007: 38th of 119 teams in CFB at Indiana
2008: 97th of 119 teams in CFB at Indiana
2009: 84th of 120 teams in CFB at Indiana
2010: 56th of 120 teams in CFB at Indiana
2011: 12th of 120 teams in CFB at Northern Illinois, 12th from the year before and 13th the year after
2012: 60th of 124 teams in CFB at Wisconsin, 6th the year before and 27th the year after
2013: 98th of 125 teams in CFB at NC State
2014: 57th of 128 teams in CFB at NC state
2015: 41st of 128 teams in CFB at NC state
2016: 68th of 128 teams in CFB at Pitt, 46th the year before and 10th the year after
2017: 76th of 130 teams in CFB at LSU, 68th the year before and 38th the year after
Then in 2018, he was Maryland's head coach and led them to a 5-7 record and 69th in points/game. 3 of his 4 1-year stops had teams where their offense was better before and after he left than when he was there, and the 4th was just equal in all of those. The only place he actually showed any progress in improving offensively is at NC State.
Frankly it's bizarre that he's a NFL OC to begin with, let alone one people argue against being the primary cause of problems with this offense. The dude is a middling college OC at best.