I understand the OP's point and it can be infuriating. The core issue for me is a lack of transparency and consistency.
I shouldn't have to fly on Sri Lankan (BKK to HKG) to get a reasonable J class fare. I suppose it is all about timing. I recently purchased a TG business seat to BKK from HKG and it was literally half the cost of Cathay.
And yet, when I look at equal quality airlines like OZ or AF/KLM or even the LH Group on the CDG/ FRA routes, TG is nowhere close.
I get the feeling that TG prices based on the distribution channel one uses. Would I be wrong to ask if purchasing from certain agents allows access to lower cost premium class fares?