I've flown KE's 777's and MH's 737. I feel KE's seats and service is better than MH. KE's ICN J class lounge isn't the worlds best, but certainly rates in the top 10. The ICN airport is world class with much to see and do and rapid access to Seoul.
MH offers a good product. The satay serving is unique. The Golden Lounge at KUL is OK but nothing special.
So is KE $400 better than MH? I think so. At least I'd pay the extra one time to be able to experience ICN airport and lounge.