Nirvana in Fire is considered the best but Nirvana in Fire 2 is probably easier to get into, it's more standard, has more romance and focuses on family, in addition to the usual things.
Compared to most historical dramas, Nirvana in Fire (1) is darker/more realistic, more plot-driven, deeper philosophy/politics, and has this psychological aspect to it, think Dorim from Soo Baek Hyang but better. Overall it takes a new approach to historical drama so be prepared to change your mindset while watching it, many people have trouble getting through the early episodes. Some people see it as the Game of thrones of China minus the sex, and while I mostly disagree, I can see why people may think that way.
Other recommendations:
Most similar to Empress Ki/Moon Lovers:
Prince of Lan Ling
Legend of Lu Zhen
General and I
Scarlet Heart - didn't watch it because of the hairstyles and Cecilia Liu but I assume it's as good as Moon Lovers.
Other Historicals:
The Myth - Hu Ge and time travel
Princess Agents - Strong female lead.
Perfect Couple - comedy
Tribes and Empires: Storm of Prophecy - has moderate amount of fantasy
* All of the above contain little to no fantasy except Tribes.
Seeing as you've watched Battle of Changsha,
World War 2 or period before it:
The Disguiser
Lady & Liar / Cruel Romance - Very similar to each other, I prefer the former
The Red
Too Late to Say I Love You
This thread might give you more suggestions: https://mydramalist.com/discussions/chinese-drama-movies/30266-historical-chinese-drama-with-less-fantasy-elements