A Rails project I'm working on has this LOC
Ruby 12169
ERB 2339
Vue 24895
Js 4526
The Vue frontend is indeed more complex than the Rails backend, and in my experience Vue is much simpler than React. My customer organized the Rails app with models, controllers, api/v1/controllers, jobs, services (naming only the most important stuff). It's not bad to work with.
The language and framework are both centered around developer happiness, which in my experience drops off around 10,000 lines. That's about when projects start getting difficult.