Takeaways are relevant but giveaways aren't?
Yes, players who have the puck more tend to lose it more, but it's still valid in perspective.
Over the last five seasons, Matthews leads the league in takeaways (336), with Marner second (331) and Nylander eleventh (258). At the same time, Matthews is 51st in giveaways (236), Marner is fourth (345), and Nylander is 134th (179). Obviously not all the players who handle the puck a lot lose it as much.
But my point wasn't really about Marner at all - looking at the top players in takeaways, many have a similar number of giveaways (as does Marner), but a few have appreciably fewer. Mark Stone and Nylander are the only ones with fewer than half the giveaways. Also, Willy has been improving on both the number of takeaways and the ratio the last few years. As I said, my point was that "I don't think Willy is as bad defensively as some people would like to believe."