Not all that unusual for MP airline partners though: JL and QR have MP business class fare buckets that earn under 100% RDM/EQM. The lowest SQ J fares earn 100% EQM/200% RDM. Certainly no BA or even AA but not actually bad like that (other partners have comparable EQM/RDM earning).

I can certainly see why if you're not headed to Singapore (or using it as a convenient spot on the way) and you had a miserable experience (and there are better earnings on other airlines you like better) you wouldn't go out of your way to try SQ again though.