"They can't find a way to make Baizuo a protected category, which stops them completing the system of German Idealism."
Isn't that exactly the trick?
You make your manservant and your groundskeeper protected classes. You send them to do all your errands, so in practice that makes you the protected class, as is the historical norm. However, by adopting the appearance of protecting the lower classes, criticism of the class system is deflected. Indeed it becomes easy to deny that there is a class system at all
Naturally anyone who refuses to be your manservant gets ejected, in practice, from the protected classes. Pro forma they match the definition, but everyone important - such as the manservants in charge of deciding when a protected class' protection is threatened - is told they're "Uncle Toms" or have "internalized misogyny" or whatever. Anyone who doesn't know what these euphemisms mean and protects an outgroup member is simply fired and themselves made outcast.
The only cost is making certain protections somewhat awkward. Sometimes the peasants notice that the police protect CNN and your gated community, for example, while allowing your manservants free reign to commit any crime they want in the peasants' neighbourhoods.
Occasionally someone stumbles upon a direct insult that can't be linked to attacking the 'protected' classes, but ignoring those just makes you look magnanimous, doesn't it? Though it is certainly annoying.
Luckily figuring out the protected classes are all slaves (more directly than usual) of certain other classes would require seeing an inferential step beyond the childishly obvious, and is well beyond the capacities of the supermajority of peasants. The scam is quite secure.