Hm, I never found adding custom routes to Rails painful - could you elaborate? Anyway, for smaller use cases I found Sinatra + ActiveRecord a great match.
Sinatra is awesome! Had a project recently where Active Record and Postgres with Sinatra made sense and it was completely painless.
Rails _might_ have helped, but I have come to enjoy Sinatra's flexibility. Been debating about making something in between, but working on other things.
I'll be frank, the latest Rails version I used was Rails 3, and it was like 6 years ago, so I can't really remember details, except that I had to spread logic to like 3 files to make it work. Maybe things changed.
The whole point of my example was that it is possible to do resourceful routing in a single file without having to resort to using custom routes. I try to avoid custom routes whenever possible - in my experience they lead to pain in the long run, more often than not.
Rails _might_ have helped, but I have come to enjoy Sinatra's flexibility. Been debating about making something in between, but working on other things.