yes, reducing round trips is very important for web performance. It can be done via a server-side architecture where external resources are sent immediately as prefetch headers, then the page is generated and sent after database calls etc are made. Or via a client-side architecture where API calls needed for initial render are either sent via prefetch headers, or included inline in the HTML response.

If you don't need page interactivity then a pure server-side approach works best because you do not need to send, parse, or execute any page logic. For highly interactive pages you tend to need all the logic to rerender each component on the frontend anyway, so client-side rendering makes sense as a simpler approach without significant performance costs. Isomorphic approaches are more complex and brittle, they tend to hurt time to full page interactivity because of duplicated work, but can be needed for SEO. Reducing overall page weight and complexity and lazy-loading where possible, and getting rid of the damn tracking pixels and assorted third-party gunk, are often more effective directions for optimization than worrying about where HTML is generated.