They shouldn't have had made Wol Ah / An Shim be played by the same actress regardless of their intent to have have them share resemblance to one another. Wol Ah had her own role and was a turning point in the story. Since An Shim came to the picture, up until the end she was nothing but Wol Ah's replacement and had no real character. The drama, unsurprisingly, shared a common problem with others of the same genre. The drama started with the backstory and the hero journey but later on it striped the personal attachments and turned it into a battlefield between nations instead of mixing both elements together. It got turned around the other way back and forth 4 more times, making each transition more jarring than the last. This is why there was a massive disconnect after the timeskip in the early second 1/3. In addition, the last 15 episodes were too long to endure.