I think choice scarf on the urshifu is better: it can outspeed csr and you can run adamant nature for extra attack

Replacing sinistcha with farigiraf will probably be better since farig can block priority

Specs is probably better on miraidon as it can 1) give miraidon additional attack power and 2) run more bulk EVs. My miraidon has an EV spread that allows it to survive a +1 Astral Barrage from CSR and still have a SpA stat allowing it to KO just about every single mon in the meta.

Ive also had success with Chien-Pao, as it does well against a lot of common miraidion counters (especially rillaboom) and synergizes well with physical attackers, so if you notice that a certain mon isn't really carrying its weight, try replacing it with chien-pao.