You can tell that this is happening because there is a 1:1 mapping between foos_controller and views/foo.
There's nothing wrong with MV code and it's a great paradigm for a simple app. But lots of rails apps are no longer simple...
It's possible to implement a proper separation of concerns and clean architecture using Active* modules, but Rails actively encourages bad design. I still like Ruby, and there's a lot of good software within the Rails ecosystem, but Rails itself is poorly-architected and encourages bad design.
How you achieve this depends upon the language. One thing I like to do in statically typed object oriented languages is to use classes for basic data rather than spread primitives everywhere. This makes it obvious where to put validation - e.g. the PhoneNumber class in the model will necessarily ensure the data its passed isn't bad. Repeating that logic in a controller or view tends to be a poor decision.
Rails has done so much to move application development forward, but if I had two nits to pick, they are the same today as they were in 2007:
1. Assuming/requiring a folder structure named after the pattern an object fits, rather than conceptual domains of an application.
2. Naming its templates "views", and not hinting to people that presentational logic should belongs in a full instance of a class, rather than in-line in template code. Partials help but insufficiently, and helpers have too many gotchas.
The sprawl of gems that attempt to address #2 this is evidence of its impact. While I appreciate the "omakase" argument, it still leads a lot of smaller or less-experienced teams to make a big mess before realizing they have better options.
Anyway, as often as I see "service objects" solutions helping a team tame their Model-View-Mess, just as often I see the solution lying in adding an actual View layer (or adding Presenters if that fits better).
I like ActiveRecord, ActiveRecord::Relation, ActiveSupport, and all the other things people tend to gripe about in Rails-land, but the specific folder structure has always been a stick in my craw.