>>that was just a trait adaption
You're not thinking on a long enough timeline. Now what would happen if the Moths did start producing larger offspring as well. Then those started to develop afformentioned poisons. At what point do you stop saying: "Thats not a different species, its just a different version of the same thing." Technically we're all just a collection of cells with different traits.
If we all had the same cells then why can't cats and dogs breed together? I think that genes are an important to remember.
>>The adaptations are so subtle that they disprove the theory
Again; Its the timeframe. That was an infintesimally small period of time in the "grand scheme of things".
How can anyone know the time frame? This slow evolving theory has never been proven. No one has documented anything for longer than 40 or 50 years.