Maybe if blissey didnt had 10 base def it could be a top tier wall again. Power creep happened, having a gigantic defensive stat and the other being pathetic isnt cutting anymore. The lack of ''flawless'' defensive pokemon hurt stall viability as you can always exploit a weakness and get through that pokemon with easy. You cant do that with offensive pokemon. Whats the flaw with keldeo, terrakion, garchomp, salamence, landorus etc? Nothing. They have excellent movepools, offensive stats and stabs. You are forced to either revenge kill them or hope one of your pokemons can barely take a hit and retaliate. Then go check the defensive ones. Jellicent physical bulk is terrible meaning that it either invests in that or it will fall to physical attacks easily. And even if it does its still far from ideal. We also have ferrothorn with a ridiculous exploitable fire weakness and i dont think skarmory requires any explanation. The terrible distribution of recovery moves is simply laughable, as is the lack of defensive based items. Its simple, the metagame has become offensive because offensive threats are superior to defensive ones. They require much less support and have better tools to do their jobs. This is a problem that no ban or clause can solve.