That's rather odd as I've met some Byzantine Rite Catholics who deny it is true at all.
That doesn't mean that profession of it isn't required of them. There are many Latin Rite Catholics who support the ordination of women as priests - does this mean that rejection of the possibility of priestesses isn't required of them under our laws?
The ab utroque procession of the Holy Spirit confuses the origin of that person of the Holy Trinity. Saying the Holy Spirit proceeds from the Father and the Son as from one principle, essentially says the Father and the Son are the same person.
Greek Catholics per the Union decrees are only required to believe the Holy Spirit proceeds from the Father through the Son. We only can accept the filioque if it is understood to mean that.
In any case the Latin Councils only became ecumenical as a Counter-Reformation argument between the Latins and the Protestants. If Lyons II was ecumenical, then why did Florence claim to be the 8th ecumenical council?