“Worse” here is relative to how we have designed sites such as Google maps today. The current web would fundamentally break if we stopped supporting scripts after page load, so moving would be painful. However, we build these lazy and bloated monolith SPAs and Electron apps because we can, not because we have to. Other more efficient and lightweight patterns exist, some of us even use them today.
If you can exchange static content, you need very little scripting to be able to pull down new interactive pieces of functionality onto a page. Especially given that HTML and CSS are capable of so much more today. You see a lot of frameworks moving in this direction, such as RSCs, where we now transmit components in a serializable format.
Trade offs would have to be made during development, and with a complex enough application, there would be moments where it may be tough to support everything on a single page. However. I don’t think supporting single page is necessarily the goal or even the spirit of the web. HTML imports would have avoided a lot of unnecessary compilers, build tools, and runtime JS from being created for example.