I agree with this completely. I mean there's a guy here who can show you a bunch of 'advanced' stats to justify why Marner got his contract, and another guy who can show you a bunch of 'advanced' stats to show you why he deserves another big contract but I watch the guy play, and I just don't see it. Regular season, sure he's on the fringes of being a top 5 winger, but he's not getting any better, there are always young guys coming into the league so a few years from now his ranking will likely be lower. Main thing is playoffs though, he has a big game here and there but all too often he's not even noticeable out there and for his career he's a 70 point player in the playoffs, his last two series he was mediocre at best so in the playoffs, he hasn't been even close to worth his cap hit. If the NHL was a real world job, he's be in line for a pay cut, no doubt about it.
Really the only argument that he should get another huge contract is "playoffs don't matter" when negotiating contracts. That's always been an exceedingly stupid concept for me personally because playoffs matter a lot so I say either take a pay cut or play somewhere else. Unless of course he morphs into a playoff beast next spring, but that doesn't seem likely and in any case until it happens, I wouldn't commit to him.