Tbh, she's not inferior to the emperor, they are just too different in terms of class. Of course she doesn't know much about the palace's people and their schemes, it is known that at that time the palace was quite segregated from the eye of the people (I believe the author took inspiration from ancient China/Korea), so it is not surprising really that she's lacking in knowledge (even though he says that she could be quite good if she wasn't an assassin). And about the skill: she might be famous for KILLING people, but it is never established that she is this SHADOW IN THE NIGHT INVISIBLE CAN KILL YOU AT ANY MOMENT BEWARE. You have to understand that rumours back then was very exaggerated, so I what I think is that she simply always finished the job, hence the ripper nickname. She's a commoner and a killer, she can be quick on the uptake but still makes mistakes. It's nice to not see this omnipotent mc, I had my share of those already.