I dunno. I've never heard the positive case for environment-only. Usually they just cite current limitations in the hereditarian argument and call it a day. In my opinion these really arent 'arguments against hereditarianism' per se, because the competing proposition is just assumed to be true in a very "god of the gaps" style (to reference old Atheist versus Theist debates).

These debates mostly boil down to, 'you cant be totally certain with the tools at your disposal so we should assume it's all environment.' Which is obviously silly, you dont get to assume you're the default position. Science is about determining what is more or less likely based on research, because absolute proof is hard to acquire using the scientific method. https://en.wikipedia.org/wiki/Abductive_reasoning

Granted these would be good arguments against instituting horrifically brutal policies, which I think suggests the motivation behind the people making them but they should be more honest

It's a lot of stonewalling the hereditarian position by saying they always need more evidence. First it was denying IQ matters, then it was denying race can be studied (you can think it's an arbitrary category, it still reflects some differences), then it was demanding the specific genes be found, then epigenetics was suggested as the real reason, now twin studies seem to be the target.

To make matters worse: the environmental factors are becoming more nebulous and abstract to cope with a lack of explanatory power. From socioeconomic status to 'systems of oppression'

There's no positive case made for environment-only is my point, just an increasingly higher standard for hereditarianism