Yeah this is basically it. Vercel is trying to solve for optimised performance by using a combination of React Server Components, Partial Pre-rendering, Edge servers, streaming, etc. A lot of their seemingly weird design and API decisions basically come down to that. If you need it, it's good that it exists. But you can also go pretty far with doing some ssr in an edge function too.
I would be more inclined to believe it’s an end product of years of simultaneous resume and job security driven development.
LIRPslop, as Brad Troemel would put it.