You realize that the Gnostics were condemned by the Apostles, right? In fact in the Letter to the Romans, in the Latin translation St. Paul actually says to them, “Anathema sit.”

(It’s somewhere in Romans 12, I think,)
I actually have never heard of them, but I’ll take your word for it.
There are no such things as “EO rituals” - they
retained their Catholic rituals, and continue to retain them to this very day, which is why (unlike Protestants) they don’t have to undergo a “continuing conversion” process when they enter the Catholic Church - because all of their rituals are
already Catholic, and (as a consequence of that) all of their Sacraments are already valid.
Their Divine Liturgy is exactly the same in every detail as that of the Eastern Rites of the Catholic Church. The only difference between them and us is that they deny the authority of the Pope. They only began to deny the authority of the Pope in the 1000s AD - prior to that, they were his greatest defenders. (You should read the Sermon for Pentecost of St. John Chrysostom.)