I think his effort issues are mostly compounded by his playstyle and his footspeed. I don't think he's any lazier than a majority of NHL players, but I agree that he LOOKS a lot lazier out there. Does that make sense?
When he pushes himself he can have a good top-speed. He doesn't have a skating issue that limits him, he's just a big guy who takes a while to get up to speed. When he wants to, he can catch some guys with his long stick and long stride. I saw it today in the scrimmage against Connor Brown. He is NOT quick footed though. Guys get around him, guys beat him to pucks constantly, and he can't chase someone down unless he really pushes himself. That's where the effort comes in. If he pushed himself more, he wouldn't get beat to pucks so much. He would also get more zone time offensively and would get pucks out of the defensive zone more.
The other issue is his playstyle. He likes to watch the play and make reads. This works for a slow guy like Mark Stone who gets a ton of turnovers and intercepts passes. Brown doesn't have that same feel for the game and the same anticipation defensively. As a result, he gets beat to pucks, doesn't hustle, and then watches as guys get off good scoring opportunities while he sits there, not moving his feet, looking dumb as hell. If he kept his feet moving, it probably wouldn't change the end result, but it wouldn't look so bad as watching him glide around the defensive zone 1-2 plays behind the puck.
There are guys who work less than Brown but manage due to their playstyle. Guys like Mark Stone. I also think there are also guys who are physical freaks who have insane footspeed for their size who also put in the same effort as Brown, but don't get beat as much and thus it isn't apparent that they aren't working hard. Brown has this trifecta of issues that feed into one another.
On the flipside, offensively, the Brown simply understands what to do like it is second nature. Watching him control the puck off a bad pass. or perfectly timing his zone entry to match another forward is something some guys never master. Offensively the anticipation he has to drive to the net and his instincts are great.
I wish him all the best, hopefully he figures it out, because he still has all the offensive potential in the world.