Interesting. It seems like several call sites already check the equality case:

---- setobject.h: ----
#define PyFrozenSet_Check(ob) \
    (Py_IS_TYPE(ob, &PyFrozenSet_Type) || \
      PyType_IsSubtype(Py_TYPE(ob), &PyFrozenSet_Type))

---- object.h: ----
static inline int _PyObject_TypeCheck(PyObject *ob, PyTypeObject *type) {
    return Py_IS_TYPE(ob, type) || PyType_IsSubtype(Py_TYPE(ob), type);
}
#define PyObject_TypeCheck(ob, type) _PyObject_TypeCheck(_PyObject_CAST(ob), type)


Perhaps it would be better to use PyObject_TypeCheck where applicable (such as in the type_call function you mention, and in abstract.c's binary_op1()).