Is “A increases the bigger B becomes” a legal English sentence pattern? Is it really a disguised “the more X, the more Y” pattern?

The importance of interfaces increases the bigger your application becomes

This puts effect before cause, so harder to interpret on sight-reading. All the other examples you give are "the right way round". In my opinion it's still a bit awkward with the clauses reversed, so some re-working is probably required. Something like:

The bigger the application, the greater the importance of interfaces

Or something even terser.