Of course, Abhidhamma is mentioned many times in the Sutta Piṭaka, e.g. in the Mahāgosinga Sutta of the Majjhimanikāya.
It is commonly accepted that such references in the sutta are actually references to deep/profound matters on the Dhamma, just as there is reference to abhivinaya in the suttas, that correspond to deeper detailed matters on the Vinaya (and not to some Abhivinaya Pitaka).
The fact the authors of the Abhidhamma Pitaka named it as such doesn't make it any more the teaching of the Buddha than if someone went and created a Satipatthana Pitaka and then turned around and said, "Hey, the Buddha uses the word satipatthana in the suttas... surely then the Satipatthana Pitaka is his teaching!". I know some people here find reductio ad absurdum
a little distasteful, but I think it's relevant here - particularly given your previously stated thoughts on false Dhammas being attributed to the Buddha.
Some people just like controversy. It is better to steer clear of it
Whilst I agree with this, not all genuine issues need to be inflamed to the level of 'controversy'. They can be assessed dispassionately, with regards to the facts, and without personal attacks. Personally, my interest here is not controversy but to find out what I should study and practice... not wanting to be led away from the Buddha's teaching, and not having all the time in the world to study everything that's ever been written in the name of Buddhism.
and get on with one's own study and practice.
Indeed... but what practice is that? There are many different ways to approach Buddhist practice even within the scope of Theravada. Some of the differences are made clear in venerable Vimalaramsi
's Dhamma talk. My determination on what to practice is (the lay equivalent) of what you in fact once taught me in relation to the Four Great References of the Maha-parinibbana Sutta, which give primacy to the Buddha's teaching and the discipline he taught.
If one's "own study and practice" incorporates things inconsistent with the Buddha's teaching, is this of value vis-a-vis the pursuit of enlightenment? Would we unconditionally recommend "get on with one's own study and practice" if someone were say, a member of the New Kadampa Tradition or Pure Land? The teaching (and in turn, the view) underpinning practice is essential, from my perspective. If the meditation instructions in the Visuddhimagga regarding one-pointed concentration are indeed ported over from the vedas as venerable Vimalaramsi
suggests, wouldn't that be cause for due caution? As much as I'm tolerant and accepting of followers of the Vedic traditions, I have no wish to (unintentionally) be one of them.