it just gives very similar vibes .
1. they meet in the gaming world and are experts
2. both FL and ML are both popular in both the series
3. the male lead chases the female lead
4.both are very highly anticipated and worth watching dramas

Both protagonists are immortal beings who are alive for a long time ( resurrected or immortal ) only that in rattan the fl is the immortal and the ml is the human. Both dramas have fantasy elements . The vibes are very similar . comedy, fantasy, and the same themes, but with a change of gender in favor of the female lol

Even though legend of fei is Chinese and descendants of the sun is korean, they still have a couple of similarities
1.the male leads both come close to death or die in a sense
2.the female lead isn't silly and is actually mature for once
3.both of them have very high rankings in my personal fav list ( descendants of the sun being 2nd fav in my korean list and legend of fei being 2nd in my Chinese list )
You shouldn't mind all the bad reviews as both the dramas are amazing in their own right