WP and JAM are different solutions
WP is a dependable solution for non-tech friendly CMS whereas JAM is for broader use cases. I don't think pitting them against each other is useful.
Anecdotally I agree with the findings - many apps suit serverless + Typescript. One aspect not covered is that as these applications grow into progressively more serverlesss microservices, they become more difficult to manage as a whole application landscape. That suits very distributed teams but for a maturing company that wants a handle on its whole application estate, it can be difficult to nail down.