I've been working on a legacy server-rendered app that has a bunch of ajax calls, and stock web components and their shadow DOM has been super helpful to keep the mess at bay. Most of the work is actually making the app more accessible, actually.

The trick is that the components really do need to be self contained, and you need to use slots and custom attributes to bridge the gaps. Styling is the most annoying part for me, but I just include the same global imports that the main page has.