Yep you pretty much nailed it. He has a ton of physical gifts but he doesn't have the natural talent or IQ to let him rack up points while half-assing shifts. For him to put up points he has got to be using his physical gifts to their fullest and be scratching and clawing out there for every point. When he is not going all out it shows. Most top point producing NHL players have that x factor that lets them cruise at 80% from time to time and still be putting up points, this happened on the Jets with Connor and even on the Kings with Fiala both of whom have bad games where they are not all there but end the night with 2 points. PLD doesn't have that "easy point producing" ability, when he is putting up points esp at 5v5 he has to work and go as close to a 100% as possible and scratch and claw out there which he sometimes doesn't do.
I think that is why he frustrates fans, when he going all out he looks like a top level 1C in the league, but he is either unwilling unable to do that for big chunks of the season and when he's not doing that he looks like a pretty mid 2 C.
If Kings can keep him motivated or help him find that level esp during the critical portions of the post season they'll get good value from the player.