The biggest similarities between these two dramas are the high level of comedy and the fluffy romance. Both don't take themselves too seriously and the characters are very funny, peculiar and adorable.
Both are about characters in a comic changing their fate. Rewriting Destiny is Chinese well extraordinary you is Korean. Both are love stories with a sick female lead.
The same concept that the character dies and come back to the plot for a different version. In hoth cases FL is ar ghe same time the scriptwriter and the FL from the subplot and ML start despising FL for larer falling in love with her.
Both dramas are set within the world of a manga with a self aware FL. Both FLs are supposed to be murdered by the villain ML, but resolve to change the story/their fate, and end up falling in love with the ML. Both FLs are ill and can only be cured by the ML.
Both MLs are talented, seemingly cold doctors who lost their mother tragically, and the FLs are suffering from a rare illness the ML is attempting to cure.
Both dramas begin with the FL being betrayed, then getting a chance to change her fate when she finds herself either back in time or in a parallel world.
Both FLs are self-aware characters doomed to die in a historical novel. Despite this, they decide to fight their fate. Both MLs are morally gray and an enemy to the FL at first.
Both dramas feature contract marriages that turn into true love. Both couples run cosmetics/skin care product shops. Both are historical dramas with a modern mindset or twist, and are female-driven stories.