I've always been skeptical of this QoC relevance when it comes to measuring production. You're on the top line, so you're up against the other teams top line, OK in a vacuum that sounds relevant. But the top line you're facing isn't always out there to shut you down, more often than not they're trying to score as well so no reason to assume they're super hard to score against. And of course some teams are so bad that their top line kind of sucks anyway.
Willie over the last 4 playoffs has IIRC only one less point than Marner, he doesn't get to play with the goal scoring machine that Matthews is and with Marner getting substantially more ice time on top of that, I don't think there's any question who's been more dangerous offensively. Marner is better defensively of course, that's not even a debate IMO.