The "competing" vs. "not competing" argument is a lot more nuanced than I think you are making it out to be. On the one hand, if you are simply equating "competing" with "visibly putting in effort on the ice" then I agree with you. Because I think Pettersson truly is trying when he is on the ice. He's obviously lost a ton of confidence, but I do think if you asked Pettersson whether is is giving 100% he would say yes. And I think that may be correct.
But I think "competing" is a lot more wholistic than that, and includes off ice preparation including both training and mental preparation. The "competing" doesn't just start on the ice, and in fact, never really ends. And I think most players in the NHL, and certainly most top players in the NHL, needs to be constantly "competing" and trying to get better day after day, and in fact, I think it is only those players with an incredibly high standard of success that are able to continue to excel and in fact improve. You can think of players like the Sedins that really demonstrate this quality. And I think if you don't have this high standard for success, and don't consistently apply yourself towards that standard, then you will regress even if you look to be "trying" on the ice.
And unfortunately, the regression isn't overnight, its a slow steady process. So a player can continue to get statistical results, for the most part, while this regression sets in. And then the statistical results start to wane, and the player enters a slump, and it becomes really difficult for the player to work himself out of hte slump as he has slowly regressed for days and weeks.
And this is what I think may have happened to Pettersson and I said this much months ago, and the pro-Pettersson crowd laughed at me. But, since then, Allvin has publicly came out and made very similar statement.
So, to make a long story short, I agree that Pettersson is "trying" on the ice, but I don't think he is "trying" or "competing" enough from a longer term wholistic approach. And I think this is why Pettersson hasn't been benched because there is no singular moment where he's given as bad as an effort as Miller has.