I am curious to see how many HN-reading developers agree that big-O "really means" or "should mean" an expression of exact complexity (like theta does tradition

I am curious to see how many HN-reading developers agree that big-O "really means" or "should mean" an expression of exact complexity (like theta does traditionally). I disagree. There is an extremely active world of researchers and many (I believe) developers for which big-O definitely and clearly means "upper bound" and not the stronger theta notation. Basically all research papers in CS use O as an upper bound, and those, to me, are the definitive active voices. Beyond that, purposefully confounding O and theta is actually clashing different ideas together - ideas that have been separated for their utility. Often knowing the O notation requires some thought, and knowing theta is even harder; in practice what is most concerning is an upper bound, so that idea is important and useful. If the default object in language became exact complexity (not an upper bound), our lives would be much more difficult -- the practical thing to talk about would end up being whatever new notation replaced the idea of upper bound for complexity (aka the "traditional" big-oh).