Vatican II was a watershed of openness and sympathy for the eastern rites (as they were known at the time). The voices and opinions of the Eastern Catholic participants, especially the Melkite patriarch, were heard as if for the first time, and some of their suggestions were taken seriously.
It was also the time when Cardinal Slipyj was released from the Gulags, and he was something of a happy media event. The church was beginning to see itself as something more than the Latin rite with subsidiaries. I once had a set of vinyl recordings of the many liturgies celebrated during the Council, I think there were six including the Ambrosian and the Mozarabic and the Byzantine-Slavonic. The Fathers of the Council really expressed a lot of respect for this diversity (and perhaps a bit of regret that things had not gone so well in the past). Cardinal Montini was himself from Milan, where the Ambrosian rite was originally native (actually all of north Italy, but reduced to a few parishes in Milan by that time).
One result was the issuance of
Orientalium Ecclesiarum (the decree on the Eastern Churches) which was a landmark document for it’s time. Every Eastern Catholic should read it. Then Pope Paul VI met with patriarch Athenagoras (I think before the Council completed) and the very important mutual lifting of the anathemas which followed made dialog with the Orthodox possible.
When Eastern Christians think of the Spirit of Vatican II, these are the things they will think of most of all, and almost no one would want to turn the clock back on it.