Opponent quality is relevant. It's pretty natural to see lesser production against higher quality opposition or higher quality defenses. But Matthews doesn't seem to have any unique issue with this. He produced well against playoff teams this year, and he produced well against past playoff opponents in the seasons he faced them.
Matthews' career playoff production has been impacted by a number of things, from starting so young against the behemoths of the hockey world, to injuries and the goaltending he's faced, and more. It's not any one thing, and there have been times when he's produced very well. Even when he's not, he still gets chances, his line still gets chances, and he still drives and controls the flow of play and tends to outscore the other team. He still goes to the dirty areas. He still battles along the boards. He still plays defense. Hits. Blocks shots. Etc. I'd be more concerned if everything fell off, instead of just conversion. And even continued conversion struggles would be more concerning if it didn't correlate so well with his injuries, similar conversion struggles throughout the rest of the team, and similar conversion struggles by other teams that face the same goaltenders after us.
Pretty much everything points to either external goaltending impacts compounded by injuries and/or a systemic issue much more than a player issue.
