I would argue that subtype polymorphism is functionally equivalent to Ad-hoc polymorphism especially in the presence of multiple inheritance.

The distinction is how polymorphic code is written not what the semantics can be expressed. E.g. rust traits allow for dynamic dispatch. While there is a distinction between ad-hoc polymorphism and subtype polymorphism, I don't believe it is necessary when comparing what semantics FP and OPP languages express.