> Then you add a couple of client-side Stimulus controllers, maybe a Turbo frame here and there and it works fine, but then you get to browser navigation and you're screwed, because none of this works out of the box if somebody were to submit the form, then navigate back. Now you have to implement lifecycle handling to account for navigation and once you're done, you've basically implemented a SPA, except it's broken into a mix of tightly-coupled Javascript, Ruby and ERB templates.
Where in this process did you need to start adding navigation via JS? Did that functionality really require JS, or was it implemented that way just because other parts are JS, and the trend was continued? Could you have used Stimulus controllers to manage functionality on the page itself, but when it came time to navigate to a new page, just done a basic browser redirect?
Saying that SPAs is a mistake doesn't mean that a strong dependence on JS or frameworks in a mistake. It just means that trying to make an entire site fit into a single page load introduces more costs than savings. You can still have pages controlled via React or Vue or Stimulus, but forgoing the router functionality.
In my own apps, I use Vue and VueX to control page behaviors, but each URL is its own Rails page. For example, I have a search page that uses Vue and VueX to asynchronously load, filter, and display search results. Clicking on a result is a basic browser redirect, taking you to the result's page, doing a full Rails page load, and again using Vue and VueX to manage any dynamic state (any static content is rendered via ERB files).
This has created a very clear and simple structure that allows each page to have any dynamic functionality it needs, but no complications from having to maintain navigation or browser history via JS. The browser already does that natively, and I get to spend my time working only on actual features--not recreating the browser's built-in functionality, or debugging my own take on it.