But that's kind of the point. Yes, linemates will affect ultimate totals, but it shouldn't essentially be the magic wand to explain away why Matthews still hasn't surpassed 29 assists or on pace for less than 40 assists, if his playmaking is as good as some insist.
Case in point, in 2015-16, Crosby was still able to register 49 assists despite being saddled with the ghost of Chris Kunitz as his most common linemate that season. Kunitz's production was no better than Hyman's that year, and his overall effectiveness at finishing chances was about the same.
I'm not trying to rag on Matthews' playmaking here, but I do think Hyman being used as the main reason his assist totals are really low for a supposed good playmaker is getting overplayed. Other players have been saddled with less-than-stellar finishers (Crosby, Malkin, McDavid) but that didn't result in them struggling to register 30+ assists.