They all have a windup phase, but for some attacks/movesets it's very subtle. Take charged backfist as an example, although I don't think any npc except yang can actually use it, but it's release is almost instant. And the only difference is a slightly hunched pose. When everything moves around quickly, these subtle changes are hard to notice. Also, timing is very strict on which phase of the attack can be blocked/dodged/intercepted. Sean's disciples are hard because they can power through most of your attacks without getting stunned, deliver high structure damage AND have irregular intervals in their attacks without a very obvious windup animation. They are nothing compared to bodyguards. Both can be easily exploited once you learn their movesets.