Well, Milotic's a defender whose ability is based on moveset, once thats figured out, it falls like a house of cards and its sets tend to be nonstab, but blastoise may be better, it has good defense so I can take some hits, and with the rock and ground types players tent to use in gyms, those will get hit hard.
It could be good, but like all defenders, it would require some gym partner synergylike being along side pokemon weak to ground/rock/fire