This YouTuber is not particularly knowledgeable about either Delvaux or Hermès, which to me detracts from her credibility. That said, yes, Delvaux bags on the second-hand market can cost about half the price of a new bag. They aren’t status symbols like some other brands: they are more quiet luxury, under-the-radar. Therefore there is less demand for them on resale.
Personally, I don’t buy to resell, so to me the transactional value is not important. I’m trying to build a collection of Delvaux, buying a couple bags/season that best express to me the theme or spirit of that particular collection. I couldn’t do that buying on the resale market.
So it It all depends on your goals and shopping habits. I’ve never bought a used bag of any brand. This is a personal choice, with no judgement of those who do.
One of the drawbacks of buying used is authenticity. In the video in question, for example, the large, pink, slouchy “Brillant” with a very small buckle was a really bad fake.