I don't think the unnatural English is a product of cross-translation so much as it's a product of not having a better proofreader aboard to clean up the awkward phrasing, references to people by their names when second person would be more appropriate, etc. The manga would benefit far more from a better proofreader at this time than a TS or even cleaner/redrawer, especially since this series is very plot- and character-driven. I'm not sure if there are other dynamics at play -- I've personally worked with (against?) TLs in the past who were insistent upon keeping stiff or awkward lines because it was a more literal translation and therefore "closer" to the intent expressed in the original language (hint: that's not how TLing works outside of high school).
The volumes these scans come from are indeed from the Korean release of the manga -- that's most definitely Hangul on the volume cover and in the SFX.