That’s not what the twin studies have shown. It’s not only the most extreme cases, it’s anything short of the very good circumstances. For example, the stable homes families have to prove they have to adopt.

Cyril-f “twin”. https://www.robkhenderson.com/p/no-one-expects-young-men-to-...

That's not true, for example metacognitive ability studies have shown environment plays the dominant role. Twin studies on trust provide the same, in which genetic component while large at 33% certainly doesn't indicate what you're stating that it's only "extreme cases". Even in studies re-assessing conventional twin studies and educational attainment, the conclusion was that while some is genetic (sometimes even a large portion) the correlations between a mother and father's educational attainment points to environment playing a large role (unless you have the belief that the mother and father are siblings I suppose).

You'll be extremely hard pressed to find researchers conducting these twin studies who minimize the role of either genetic or environmental impact on certain aspects in the way you did.

Lead poisoning isn't an extreme case, it's a very common problem.

Twin studies don't exclude environmental causes because twins have the same maternal environment.