If you analyse non-standard tx on the blockchain you will see that filters work as intended., in the sense that most TX mined adhere to it. Exactly what the filters where defiend for in the first place. Miners who mine non-standard tx will be punished by slower block propagation through the open relay network. This risks orphaned blocks and thats why it disincentivises them to mine spam. Economic nodes will enforce this upon the miners and the network and limit the amount of those TX mined effectivly, as emperical proof can be found on thee bitcoin blockchain.