I think you made great points here, I'm not sure how many complaints Poly has received on Discord (since it seems like it's the balance team's main method of receiving feedback) but I think that this might have slipped under the radar due to the lack of matches that make it to 9 mana i.e. no one really experiences the issue => Poly isn't a problem to most people, plus Poly isn't played in the most problematic decks.