This is tautological and therefore logically invalid. You are presuming heresy before having proved it.
it's not up to the Orthodox to prove that Orthodoxy is Orthodox.
No one would question that Orthodoxy is Orthodox, but is it, orthodox, the two are not the same.
An innovation is always considered heretical until proved otherwise.
As St. Maximus has shown, the use of the formula Filioque (outside of the Creed) is attested by all the Latin Fathers and can hardly be considered an innovation. Or do you not consider the testimony of the Latin Fathers as of equal value as that of the Greek Fathers?
For the sake of any following discussion, and in order to avoid having to always repeat myself, whenever I refer to the use of Filioque I am only referring to its use by Latin writers and not its insertion into the Creed, unless otherwise stated.
This old fairy tale again?
"The Holy Spirit in truth is neither begotten nor unbegotten, neither created nor made, but proceeding from the Father and the Son." (Creed of Damasus, 5th Century)
"The Spirit is also the Paraclete, who is himself neither the Father, nor the Son, but proceeds from the Father and the Son. Therefore the Father is unbegotten, the Son is begotten, the Paraclete is not begotten, but proceeding from the Father and the Son." (Creed of the Council of Toledo, AD 447)
"The Holy Spirit is from the Father and the Son, not made nor created nor begotten, but proceeding." (Atahansian Creed, 5th Century)
"The Holy Spirit is not of the Father only, or the Spirit of the Son only, but He is the Spirit of the Father and the Son." (Decree of Damasus, AD 382)
"And in the Holy Living Spirit, the Holy Living Paraclete, Who proceeds from the Father and the Son." (Profession of the Council of Seleucia, AD 410)
Of that last one, please note that Seleucia is in PERSIA. Last I checked, no one mistook PERSIA for a "western" land.