I agree with this. A lot of Korean NTR Manwhas don't do the NTR part very well.I think you are severely underestimating how heavy japanese ntr can get...both in Manga/Doujin and VN/RPG form. You seem like you are new to the genre so have not experienced a lot of ntr catalog of woks. Koreans Manhwa very dark works revolve around drug, prostitution, and rape not necessarily NTR and that can be applied to anywhere. Koreans at least Manhwa wise are very poor at developing ntr works. Not netori since its very easy to write netori stories. Once you read enough ntr works you will see the issues korean manhwas have.
Also, there are a lot of weak and artificial ntr works so its not surprising if you have mainly experienced ntr works focused on sexual feelings than emotional. And if someone says Manhwas have a lot NTR works..thats a red flag and it tells me they don't understand the genre and differences it has within the types.
There is one exception that I've found. A NTR Manwha that actually feels like NTR.
It is called Cohabitation:
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