It's not actually Rails that's the problem, often: it's a cultural issue. You can build a Rails app that has a very thin 'rails' layer and has a super well decoupled domain model layer.
Absolutely, the Rails app I'm working on right now is just like this. Still feels like Rails but the complex logic and interactions can run without it.
I would be interested to more details on how your architect things - we've been in the process of moving the business logic of our app into service objects as 2000 line models have become a bit unmanageable :D