I beg to differ.

There is a lot of space to cover between a bare-bones HTTP DSL (which Sinatra is) and an opinionated full-stack like Rails. For example, Padrino allows you to freely choose between a lot of Ruby ORMs _and provides support_ to use them. Try that with Rails.

As another example, Padrino allows you to do Rails-Engine-like things in a very natural way (by hosting multiple applications in one Stack etc.). It is not a Rails rehash on a different base.