Yang got smashed by a Super-Robot and then proceeded to pull it apart. And that is not the exception, from how the series pans out. That is the rule.
Actually that was the exception. Yang's semblance allows her to absorb and redirect kinetic energy. Effectively she gutted the robot with its own strength. Anyone else hit by a blow like that would be serious trouble.
Besides, logically speaking this Casino is a White Fang front. They have a lot of sensitive White Fang related stuff inside that they wouldn't want hunters or cops seeing. The most logical way to make sure that hunters or cops can't get in to see it is to make the guard at the front door someone who has the power to best hunters and cops. If he was just another foot soldier that would put the entire operation at risk.
Anyone want a "Beat Shiro's ass for free card?".
Sapphire doesn't need a free card, she's going to beat his ass at some point, it's just a matter of when and where.