As someone that develops Wordpress and Jamstack sites for a living (among other things like apps / devops), this is silly. Debating Wordpress versus Jamstack is like comparing apples to oranges. I use Gatsby + Contentful (or other APIs, like a Headless Wordpress setup) for some situations, and I use Wordpress for many companies as well. Small businesses are not going to hire a designer for PDF designs and then hire a developer to build a Gatsby site, and relearn using a CMS like Contentful instead of Wordpress. Not going to happen. For more sophisticated clients, or for building static sites myself, I always use Gatsby. These type of clients have a higher budget, and can pay for a designer and developer to build the site properly and deal with a more sophisticated deployment architecture.

Wordpress is not going away. As long as you don't have to code to use Wordpress, it will be easier and far more accessible for people that don't have a lot of money for a website to hire a web designer (lower skill, lower pay than developer).

Gatsby or another Jamstack client could build themes that don't require coding, similar to Wordpress, but I don't see it happening. Webflow is sort of doing that now by allowing designers to build websites without coding.

Ultimately, the debate is silly because Wordpress and Jamstack have two different use cases. Wordpress will probably become less popular for big companies, but it will still be very popular for your average small to mid-sized business.