> how most people use the wordI don't know about "most". The very first meaning (1 a) in your reference is "having monetary value", which is how I have been using the word.
> Artists do not provide valuable work...their work is of (very) low value
Maybe not in your subjective judgment (and both of the definitions you cited for "valuable" are subjective), but other people's subjective judgment might differ from yours. Many people pay significant sums of money for the work of artists. Maybe that doesn't make the art "valuable" in your eyes, but it apparently does in theirs.
In any case, if you're going to talk about "society" as a whole, you can't just help yourself to your subjective judgment. The definition I just cited above of "valuable" is objective: people pay money for it. And people do pay money--in many cases significant sums, as I noted above--for art in our society, so I don't think you can say artists "do not provide valuable work" for society as a whole.
Yes, if push comes to shove, people will stop buying art before they will stop buying, say, food, clothing, and shelter. But in such a hypothetical, society is much poorer, so people are forced to focus on bare subsistence. But I don't think anyone would say such a society had a lot of valuable things in it--indeed, it's precisely the fact that such a society doesn't have a lot of valuable things in it that makes it poor. A rich society has many more valuable things in it than just what is needed for bare subsistence; that's what makes it rich. And people generally prefer a rich society to a poor one. Art is one of those valuable things that people in rich societies like to have. Not everyone, but people's tastes differ, and one of the nice things about rich societies is that it's much easier for people to satisfy their particular tastes, even if they're not common.