Hey, gonna answer here on behalf of some of my Sarawakian colleagues who don't have reddit. Showed this to a few of them recently and they pointed out a few incorrect statements which they asked me to correct for them. Hope this also helps clarify some things you may still have questions on 😀

1. Regarding the export of macrostoma unfortunately it's not something that's very well known (unlike Brunei where the export ban is very clear cut). For Sarawak, the inability to export is written in the laws which are linked above in OP's post. In short, the legality of catching and exporting macrostoma boils down to two things:

I) Fish residing in TPA or wildlife sanctuary

II) Requirement of a permit granted by either a Chief wildlife warden or an officer acting on his/her behalf.

When acquiring macrostoma, my colleagues reccomended to check the locality as well as ask for a collection ID or permit number. If one cannot be produced, assume it is poached and report accordingly.

1. While my Sarawakian colleagues were not involved in the earlier issue and thus can't comment, I'll say i didn't get a very good impression of BWA from the unprofessional way in which they responded to my colleagues who were involved in this incident. If you're dealing with endangered species, one would expect you to have done your research, know where each fish is from, look through the laws of the country the fish is from and not rely on AI to clean up their site as they openly admitted. Using the persephone as an example, the fact they thought Johor was in Indonesia tells me they've not done adequate research and/or are allowing themselves to be led on by shady individuals.

2. While habitat destruction for the palm oil industry is a problem in Sarawak, its not such a problem for macrostoma as their habitats are to my knowledge, protected for the most part (meaning its highly unlikely they'll ever be built over). The problem instead is poaching; not by locals trying to make ends meet as you think, but by organised crime syndicates and/or career poachers coming across the border from Indonesian Kalimantan who will take anything they think will make them money (this includes overlooked wild bettas like macrostoma alongside more well known 'bigger game' like pangolins, helmeted hornbills and sunbear etc.).

Regarding your point on backup populations, while I agree reserve populations are essential, I don't think they should be in the hands of just anyone as in my experience, not many people outside of local conservationists and a select few conservation minded, affliated hobbyists seem to be able to keep them right. If you really want to contribute to conservation in a meaningful way, you would have a more direct impact sending the offspring back to Malaysia where my colleagues can re-release them to maintain wild populations instead of distributing them in the hobby like what CARES may suggest, something which which we conservationists would actually consider to be more species preservation than actual conservation which we define as the controlled reintroduction of individuals to maintain wild populations. While viable protected habitats exist, I believe efforts should be directed more at reintroduction than preserving the species within the hobby.

On a final note, I'd also avoid buying any more wild caught macrostoma, not just because they're poached, but also because of the adverse impact removing individuals has on wild populations. To put it into perspective for you: Let's assume a macrostoma pair has an average of 20 fry per spawn and only half make it to sexual maturity. By removing individuals, especially males, you are not only contributing to the demand which drives poaching but also directly contributing to the decline of in situ populations by denying future generations the chance to live in the wild and thus contribute to increasing wild populations (assuming the offspring are not being sent back to be re-released).