Why doesn't Smogon implement the Pentagon rule in their metas? Realistically, it's the only way for Game Freak to remove moves from a Pokemon's movepool, and doing so is an entirely legitimate game change like removing gems was in the Gen 5->6 transition or the ability nerfs were in the Gen 6->7 transition. Gamefreak metas don't have to deal with Chansey and Mega Kangaskhan having Seismic Toss until the end of time because they simply mandate Chanseys and Kangaskhans have to come late enough that they don't have access to those moves; that's an entirely legitimate balance change, and one that will never be seen on Smogon without the Pentagon rule being implemented.