Well..Technically Blissey can know every move Chansey can seeing as it evolves from it. Chansey with Evolite can have a max S.Defense of 508.5, the Max Defense of 178.5(Still low), and the Max of 704 HP. Blissey has the Max S.Def of 405, the Max Defense of 130, and the Max HP of 714. So overall Chansey is significantly more bulky however, Blissey can use Leftovers, or in fact any Item it wants while Chansey is stuck with Eviolite. Blissey also has a usable S.Attack, that can be further boosted by Calm-mind, Chansey has a very poor S.Attack.