If you were instructed that the Decalogue was the Catholic method of living a moral life (and especially if you were instructed that ecclesial laws were such), I feel sorry that you experienced that.  All of the commandments are available to us by reason alone so, although the were revealed, the response of our conscience should always be one of love toward God and neighbor.  My earliest instruction in the 40s covered the Ten Commandments, but we knew that these were a convenient skeleton for an examination of conscience; not an all-encompassing set of regulations.
I think you need to review your understanding of Thomist theology or summarize it differently; as it reads, it is incorrect.  Being a faithful follower of Jesus has no meaning without authoritative guidance to what is required.
It's true that there are plenty of theologies from which one may pick as one chooses.  My reading of many of those makes me question whether any move us closer to God or further from Him.