There are irreducibly complex systems.
No there are not.
I don't think you're generally supposed to reply to such admin messages, but...I think he meant that there are systems that are irreducibly complex in such a way that, if you were to start "shotgun debugging" or to metaphorically take a pickaxe and start removing pieces, they would fail to work.
That's a different thing from saying there's no way it could be simplified - so as long as he meant the former and not the latter, then he's right