Interesting to see the SQ menu compared to LX. Yes, LX outshines SQ on this short route.
Here's the thing, though: The LX flight time on SIN-BKK is not very convenient, either for business or pleasure, if you're going for a weekend you don't arrive into BKK until after 11pm. So SQ is an excellent alternative!

Plus, ex-SIN you can BTC as well.... ex-BKK the only special meal in F you can order on SQ is the Japanese Kaiseki meal, which is nice. I've done that several times.
So, maybe and SQ flight ex-SIN on the way up to BKK, then LX back?