My favorite phrase to use for these situations is “I imagine”.
Anyway, so according to that article you linked to, “presumptuous” doesn’t mean what we thought it meant? Good to know. I like to restate a thing as a rhetorical question in places where it might seem presumptuous to make assumptions. :) And just to make sure, I’ll often limit myself to speaking in the first person so the reader or listener will know that I am merely expressing a limited point of view (and if I’m really scared of coming across as presumptuous, I’ll hide contentious points in brackets, in the hope that they will seem less opinionated).