I'm still not really buying the whole "Pominville wears out after 20 games" thing.
The drop off is obviously more because he got moved off of Eichel's line... which I'm not entirely convinced happened because Eichel's line stopped being effective. They've been beasting all year regardless of RW and Jason, for all he lacks at this point, was a good compliment to Jeff and Jack.
IMO, and I think it was the case last year too, he got moved off to help Reinhart get his game going and/or part of a greater roster shake up. Assuming Reinhart can be effective elsewhere (since Pominville clearly can't), they need to leave the J. Crew together and we can watch how Pommers magically becomes less old/tired.
Go look again. Poms stopped producing last year and got moved off the top line. The same thing happened this year. He's got about 20 good games, if that, then he is spent.