Typeable can leak information about instances defined using DerivingVia

{-# LANGUAGE GADTs #-}
{-# LANGUAGE DerivingVia #-}
module TypeableVia where

import Data.Typeable

data Typed where
  Typed :: Typeable a => a -> Typed

class C a where
  foo :: a -> Typed

newtype T a = T a

instance Typeable a => C (T a) where
  foo = Typed

newtype Foo = Foo Int
  deriving C via T Int

bar :: C a => a -> TypeRep
bar x = case foo x of
  Typed t -> typeOf t

-- bar (Foo 1) == T Int

newtype Foo' = Foo' Int

instance C Foo' where
  foo = Typed

-- bar (Foo' 1) == Foo'

At first glance, the instances for C Foo and C Foo' seem like they should be identical, but they are in fact quite distinct.

I'm not sure what exactly can be done about this.