You do not pull schemas dynamically. Schemalocation beyond editors is a pure theory thing. It is not default, it cannot be fast. Any serious developer has the schemas as files in their code when checking the data for compliance.

Basically, in a static typed language you decide for schema checking or not - like for Json -, serializing in structures or access in an API - like for Json.

It is just that JavaScript maps json directly in their dynamic object, array and native types. For xml that is an mismatch. For static languages both are an mismatch.