I don't think you're understanding or reading what I linked to. The entire innerHTML of the page is not getting updated. If it was a page showing emails and there were next/prev buttons, next could trigger just the div (or area of the page that shows the list of emails) to reload with the server determined next 25 emails in an HTML snippet. The navigation areas don't change at all on the page, the page and browser don't go through a full refresh at all. There isn't a payload of JSON objects to parse and store in memory, nor a set of APIs to build on the server that output JSON.
Frontends have not exploded in complexity, they are still manipulating a DOM like they have been for 25 years. Complexity was writing different JS implementations for different browsers like Netscape Navigator 4 and Internet Explorer 4. I think a lot of frontend complexity is simply because of JS framework proliferation and a stance that the entire application should be JS in the browser, a full MVC framework when the backend is likely a full MVC framework already and has to validate all the inbound data changes.
What we're arguing about is mostly preference at this point. Please check out what different server frameworks do, there are server side JS frameworks too. If you're building simple web sites (like a pizza restaurant) vs. building a web application (like an app that processes millions of financial transactions per day) then the approach is going to be different and there are trade-offs to be made when picking a tech stack.