Pre-Covid I travelled to BKK a lot, and found I preferred to be on DL metal as much as possible.

The biggest issues with KE for me are that 1. The cabins were quite warm. 2. Seat assignments are almost impossible to confirm in any cabin, and as MSP stated, DL customers are likely to be moved around for KE elites. 3. I found the food/beverage service to actually be substandard on KE compared to DL (I know many will disagree with me here, but just stating my opinion).

Again this was all Pre-Covid. The issues above are relatively minor, and I have no issue flying KE from ICN-BKK, just would prefer to avoid them for the TPAC segment.

Ultimately make schedule your defining factor. I once did a 1 hr 10 min connection in ICN in order to take DL on the TPAC segment, and found things quite rushed.