@BobbyClarkeFan16 I really like your post, and it did make me curious. I went and combed through highlights of power-plays from the last 15ish games, and I have to say that I'm not so sure it's about how bad Rocky Thompson is as a coach. I saw a bog-standard 1-3-1 from the Flyers PP, so it's not like he has them doing something very different than what it is the most commonly-used system.
What I did see:
-Owen Tippett wasting shot after shot, no matter if there were defender blocking the lanes, and whether or not there was a net-front to bang in a rebound on the off-chance the shot actually gets through. Honestly, I think that the PP doesn't lend itself nearly as well to his skillset as does even-strength, where he generates chances with his speed through the neutral zone.
-Morgan Frost getting out-muscled and out-reached in board battles.
-Bobby Brink getting out-muscled and out-reached in board battles.
-Jamie Drysdale. Another guy under 6 feet tall and 185 lbs.
-Sean Couturier, who has the size but not the feet.
This is a mostly short and underweight group who wouldn't be getting 1st unit PP minutes on good teams. Size without skill is a total waste, but skill without size places limitations on matchups and roster building. Small players can be effective, but small teams (or in this case, special teams groups) are too easy to neutralize.