My perspective is that the Abhidhamma Pitaka constitutes a Dhamma Theory that attempts to systemise the teachings of the Buddha (as recorded in the Sutta Pitaka) in such a way that they capture the technical essence of the teachings without reference to conventional concepts or references to self. Quite possibly it was a reaction to heretical monks and rival early schools who insisted on the existence of some kind of atta, puggala etc. In turn, the Abhidhamma would be classified as Buddha Word because it was well spoken.
Origins aside, I think it's a very valuable and complementary tool for understanding the doctrines of anatta and anicca. My concerns about it are when it extends beyond the scope of the suttas, presumably to fill certain gaps in a well-rounded and comprehensive Dhamma Theory that couldn't be satisfactorily answered by the suttas alone. Using the Simsapa Sutta as a guide, I believe that things that the Buddha didn't teach can be safely left to one side, so whilst I find the Abhidhamma interesting and insightful, it doesn't play a central role in my practice or understanding of the Dhamma.