> "Honestly, none of the real value was in any of the web apps. The value was in the backend logic (if there was any significant business logic at all) and more so in data and real system design, balancing between function, redundancy, resiliency, extensibility, and some notion of scalability depending on who the customer was and what expected or unexpected scenarios could arise and how our systems would behave."

These are all responsibilities on the frontend as well... Website =/= Webapp. It almost seems that a lot of backend developers are not making this distinction nowadays, even though SPAs are already out there for years.

In the frontend there is the ever-responsive UI workload, the option for web workers, and service workers are on the rise. To keep your state there are JavaScript objects, web storage (session- and localstorage) and IndexedDB. WebGL anyone...? Newly developed JavaScript should sometimes work in the browser as well as in Node.js. I am solely mentioning technology here, not any implementation - this is thanks to the frontend of the web, as sandboxed app platform (and JavaScript), being so versatile. Next to the system design of the app there is also the gap to its UI/UX design to fill. ...All should work reliable on devices with very limited resources, as there is no option to scale on the client side.

"How to reach offline functionality?" Is a question with all of the complexity belonging to the frontend. Whereas the frontend is the data's real-time interaction, the backend becomes more the reliable async distribution of data. I'm sorry, but frontend app development is everything except from boring for me.