I understand your point, but I still can't compare faith and moon lovers to empress ki and seon duk. There are all great dramas (I haven't seen faith, but I did watch moon lovers and liked it a lot), but from my point of view the difference lies in the fact that both faith and moon lovers are sageuks with a strong female cast, while empress ki and seon duk are sageuks who are centered on them and their development as main leads. When I think of moon lovers, I think of both IU and LJG, same goes for faith / LMH, but when I think of seon duk, seon duk and mishil are the first to stand up. Don't get me wrong, I love sageuks and historical dramas and I'm not bashing moon lovers (like really, I did enjoy that drama a lot and I also think IU's character was pretty strong), but she didn't carry the drama alone, it wasn't really about her, but about her supporting the male lead's faith throughout the story, opposite to empress ki and seon duk, where the male leads were there in order to support the female cast. This is my take on things, at least.
Another nice drama with a pretty strong female lead is King's Daughter, Soo Baek Hyang (2013).