No, I think (I also keep to scientific and regulator databases) that the research they use to "prove" a difference in efficacy, is research that always has to be done to prove bioequivalence or bioavailability of any generic drug, comparing between different generics and the original product.

Of course there are differences, but they are only important when switching from one brand to another, for some meds, to make sure that, say, 100 mg of lamotrigine of one brand works the same, mostly as strongly, as 100 mg of another. Some meds might "become" too toxic without changing the actual dose, just the brand.

But for lamotrigine this is not an issue.

I gave lithium as an example, because there switching may have direct negative effects. However, as we both said, measuring serum levels is the way to avoid toxicity, because individual differences matter more than excipients.