It took working in a codebase that was almost entirely spaghetti jQuery and halfheartedly-implemented Backbone for me to realize just how brittle a site is when JavaScript is the only thing keeping it working. While users operating without JavaScript enabled are probably rarer than unicorn startups, designing site architecture with them in mind has broad benefits: fast, satisfying interactions and consistently displayed information.
Server-rendered React gave us the best of both worlds. Links point to URLs that a server knows about. Forms are built of semantic HTML elements and point at endpoints that can handle non-AJAX requests. Custom tags and scrolling behavior always have native fallbacks. Modals are never the only way to access behavior, especially critical behavior like login.
I love JavaScript. It is the only tool that does what it does. And that's why, these days, I realize it's so important to turn it off sometimes.
Ignoring accessibility is a sure path to the dark side!
Good routing is your only hope of creating a maintainable website.
Be a hero. Adopt serverside rendering.
Mobile first? Sure. And JavaScript last.