The statement, "Although Eastern and Western Church Fathers affirmed that the Holy Spirit proceeds from the Father and the Son" is not true. Scripture (and the Fathers) are clear that the Holy Spirit proceeds from the Father. Christ sends the Holy Spirit, but that is different from "proceeding." The filique reduces the Holy Spirit to a junior partner in the Holy Trinity. Interestingly, the text of the Creed on the doors of the Vatican (in bronze, I think) does not contain the filioque.
There are other theological differences, mostly stemming from the western concept of original sin from Augustine. Some of Augustine's teaching are not accepted by the Orthodox.
This is an interesting revelation to me. I had not thought about it, actually. After decades as a Protestant, our Bibles called the Holy Spirit our “Comforter”. I loved that, frankly.
To your point, I read that Jesus deigns that the Apostles must “... wait on the Holy Spirit..”. That is as close to “proceed” as my reason can get at this unsophisticated level of my knowledge on this revelation that “the Son” was *added*.
I do not understand your comment that the Holy Spirit is a junior partner.
—The Trinity is the term employed to signify the central doctrine of the Christian religion—the truth that in the unity of the Godhead there are Three Persons, the Father, the Son, and the Holy Spirit, these Three Persons being truly distinct one from another. Thus, in the words of the Athanasian Creed: “the Father is God, the Son is God, and the Holy Spirit is God, and yet there are not three Gods but one God.” In this Trinity of Persons the Son is begotten of the Father by an eternal generation, and the Holy Spirit proceeds by an eternal procession from the Father and the Son. Yet, notwithstanding this difference as to origin, the Persons are co-eternal and co-equal: all alike are uncreated and omnipotent. This, the Church teaches is the revelation regarding God’s nature which Jesus Christ, the Son of God, came upon earth to deliver to the world: and which she proposes to man as the foundation of her whole dogmatic system. (https://www.catholic.com/encyclopedia/trinity)