Keith Primeau is up there when you compare his regular seasons. In 2004 people lost their mind because he was having a good postseason, but it was the only one he had. Overall he has 57 points in 128 playoff games. 18 goals. It is no surprise Detroit started winning Cups when he got traded and had Shanahan go the other way.
You can say Marcel Dionne, and I guess there is some merit there. He didn't play on good teams so you give him a break there, but he really should have had at least one great run at some point. He was certainly good enough to be a player that could do this during one playoff run.
I am more concerned about the guys who were in great situations with good teams and blew it. For that it is Joe Thornton for sure. Both Sedins come to mind as well. And I don't care how soft you are, you don't let Brad Marchand - a rookie at the time - punch you repeatedly in the face in the Cup final and just stand there like a pencil. The fact no teammates came to his defense and he didn't stop it himself was the moment I knew the Bruins were winning the Cup.
As a goalie does Luongo come into play here? And I mean as per being so skilled and having a great opportunity. I think he could fit the bill.
Right now I'd have to say the Maple Leafs core. Let's look at them individually:
Tavares - Was never inspiring as a playoff performer even on Long Island. Has had several years where he could have been a difference maker in Toronto. Lots of opportunities. All wasted.
Nylander - Might be the only one of the 4 not to make the HHOF, but he still has one playoff series win to his name. Never been a difference maker, his softness is always on full display in the playoffs
Marner - I don't know what it is, he is a great regular season player, but never scores at the moments you need him to in the playoffs.
Matthews - Like Marner, not horrible numbers. But very consistently just "meh" playoff numbers each year. Which is why they never get out of the 1st round. More than anyone Matthews can take over a series if he wants to.
All of the Leafs core still has a chance this season and following years to change this narrative. It happened with the likes of Datsyuk, Alfredsson, etc. who had a great run and it gave them a bit more of the benefit of the doubt.