McCann has a 21% shooting percentage right now and 2/4 of his assists are on Brandon Tanev goals, who has a 33% shooting percentage. Add in the fact that he is not generating a lot of chances while also giving up a lot of chances, he is in line for a major regression.
Just like Matthews is almost certainly going to have better than a 4% shooting percentage after putting up 18.5% last year and having 16% in his career.
People need to stop pretending like McCann is playing like a near-PPG player, because he is not. If he was playing in the top 6 with the way Matthews/Marner playing like they were, I wouldn't be surprised if he has the same stat-line that Ritchie is currently sporting.