I'm not convinced that it is... but it's not as smooth as client load-once rendering can be. What is/was painful was, as an example, the first versions of ASP

I'm not convinced that it is... but it's not as smooth as client load-once rendering can be. What is/was painful was, as an example, the first versions of ASP .Net Web Forms, where every client action was a full server round-trip... Server-rendered Blazor over the wire (not local or in-office server) is roughly as painful by today's standards. I do think that it's a mix... start with basic html and enhance, or start with a component toolkit with client rendering, and inject server donut or other pre-rendering. With Cloudflare and Deno, I think the latter definitely has some traction.