Of course it is a fact, it is one of the most basic laws of nature. It can be observed in interactions of other biological species not only ours. It would still hold if there were no humans. Claiming otherwise is like denying gravity.
A model working and producing a personally.desired outcome are two separate things.
The assumption of a labor shortage because of low nominal unemployment is incorrect - the gig economy is thin margin as it is even with poor pay. It utilizes the previously "idle" labor in a marginal business model but without sufficient demand in other sectors it only provides a low floor.
You are citing a political opinion from a newspaper to prove somehow supply and demand is not a natural law. What is next, an article in Astrology Today arguing 1 + 1 != 2.
[1] https://www.youtube.com/watch?v=LsUS3ynhAKY&feature=emb_logo