> So the point is to improve SEO of Vue apps

There are other points in favor of doing SSR + hydration besides SEO:

1) Reducing the amount of JS you are sending to the client.

2) Not making a SPA and keep the native functionality of back/forward behavior (scroll behavior, cached pages, forms are filled when going back).

3) Simplifying development. You don't need to manage central state anymore as you're dealing with one page at a time. You might not need an API as you're rendering the page from the server. Etc.

I've been making SPAs for years and for my current project I'm doing SSR + hydration (not using Vue) and loving it.