"Plus/minus is not a good stat, but I'm going to use it anyway..."
Okay then.
The three guys ahead of Hall in ESP last year were a combined +78 and played on elite teams with proper management and coaching. You know John Tavares has never been a plus player in his career? Career -50. Matt Duchene career -26. Ryan Johansen career -18. If you play on a bad team, chances are you're going to have a bad +/-
As for effort/work ethic... this notion only started creeping up after he came back from injury... coincidence? I doubt it. This forum is all what have you done for me lately, and forget everything else you've done up to that point in your career.
It's not a spectacular stat, HOWEVER, when you are the leading the scorer on your team AND essentially last in +/- on your team despite getting a bunch of ESP....that is not good (Perron was -16). It simply isn't. There is no way to spin that other than being a major part of the defensive issues with the team. It isn't everyone else's fault when there is that disparity. It's a "you're a part of the problem" stat.
If you play on a bad team you can also be a plus player. What the guys you list have in common is that they aren't particularly good at the defensive side of the game either. Not sure it proves anything other than bad defensive players don't tend to have good +/- numbers. Landeskog is +27 in his career on that same bad team Duchene is on for instance.
But you don't even need the stat. It's not a surprising one. Hall makes terrible decisions with the puck time and time again that lead to terrific scoring chances against. That's been a constant through junior and in the NHL.
Effort...is it injury or is he tired of it. I'm not saying he is known for lack of effort. he isn't. He isn't Kessel for instance in that regard. However, right now that effort is not there. I can't just chalk that up to injury. Injury may limit effectiveness but it doesn't limit effort. When I look at Hall right now I don't say "wow he is really trying but he just doesn't have the speed" but rather "he doesn't look as fast but he also really isn't trying so I'm not sure". It's certainly not every shift but it is enough of them to know that the problem is more of an effort one from what I see.
On the surface everyone can say "well can you blame him?". The answer can logically be "No". But then you have to ask yourself as management if you think he can get back that work ethic or if he has checked out for good. If it's the latter you can't build around him. You also have to look and see if you feel this lack of effort isn't a recurring theme at times under multiple coaches. Is it just part of his game (like it seems to be for a Phil Kessel)? Is it an anomally?
No matter what, it is IMO foolish to simply chalk it up to an injury. It is more than that.