I understand that these Churches are fully in communion with Rome but, given Rome's error, my doubts of Catholicism, for those who are in communion with Rome, are somewhat justified... perhaps I am a bit naive but, from my novice's perspective, not being in communion with Rome, appears to be a better predictor of one's Catholicism, than being in communion with Rome. Hence my question comparing them to the pre-Vatican II Roman, Latin Church.

I have an interest in understanding this as someone very dear to me might find it easier to convert from Orthodox Christianity to Eastern Catholic rather than to Roman Catholic but, before I present this alternative, I want to be sure that I am not moving towards just a different flavour of the same post-conciliar doctrines and the same lax EENS interpretation.

Officially, of course, the ECCs believe what the Catholic Church believes.

The ECCs are in communion with the Pope only as Pope. For the Roman Rite the Pope is also the Patriarch of the West and the Metropolitan of the motherchurch of the Roman Rite. The ECCs have their own patriarchs, and in most places, bishops (exarchs) and metropolitans distinct from the Roman rite bishops. (In a sense, the ECCs are free to operate almost as much as the SSPX is.)

The ECCs also have a separate canon law. They even pushed back on a scandalous allowance after V2, and Rome quietly removed it in the next revision.

They generally hold more conservative views on EENS - especially in relation to the Orthodox. But in my experience, this speculation on whether a someone who was visibly non-Catholic might be saved is not what ECC clergy are interested in. It seems to me rather a Western phenomena. I think a Ukrainian priest is more likely to say salvation is a mystery, and be more concerned about your own salvation.

ECCs have certainly valid sacraments. Some Roman rite traditionalists who don't have daily Mass go to ECC daily liturgy.