I'm not sure I buy this. I recently worked on a project where we had one .net core developer, a dev ops guy, and me doing the client SPA. We were all able to focus on our core competencies and turn around the project incredibly quickly. I would argue that you can get away with the same team size split between front and back end and possibly end up with a more efficient allocation of resources.

Perhaps, but if both teams are half the size, specialised and deliver faster, it’s a win.

That may not always be the case, but if your SSR team and API team are the same size, your devs suck, bluntly. API based backends are much easier to build, test, manage and look after.

I'd argue more than double considering all the things a good SSR gives you reliably for free.