On the contrary, as a Korean-English subber, I typically see subbers using much harsher curse words in English than what is actually said in Korean. I think that’s because most subbers don’t actually know what those cuss words mean and they are just using the most common cuss words in English, such as btch, SOB, fck, etc.
As for me, I try to come up with the closest equivalent cuss words. Sometimes, there is nothing close and I just have to go with the meaning behind, like sleaze-ball for 쪽제비 같은놈 (weasel-like dude).
When they actually say the word for btch or SOB in Korean, then I have no problem translating those words the way it is but with asterisks in between the word. The problem is though the Korean word for 년 (Nyeon) could mean, a btch, a woman, or brat or just a girl, all depending on the context. For example, a mother could be calling her daughter 미친년 (Michin Nyeon - crazy girl). So is the mother actually calling her own daughter a crazy btch? No!! In this case, the proper translation that’s has the closest meaning would be something like “crazy brat!” But subbers who are not 100% fluent in Korean just assumes that Nyeon always means btch, which is not true. The same thing goes for 놈 (Nom) or 자식 (Jashik - an offspring). A lot of people think that it means bastrd or son of btch. But it actually could mean bast*rd, a guy, dude, jerk, slime-ball, etc., depending on the context.
So it actually irks me to see those words always translated as harsher and more common English cuss words than that they actually intended to mean it.