Some of what you say is incorrect. Catholic teaching or doctrine has been the same since the time of Christ. However these teachings were not all fully understood at once but under the guidance of the Holy Spirit have been more fully understood over the centuries. The Catechisms contain the basics but not all doctrine or teaching which must be believed. We can go into that point more fully if you want but I think it should come under another thread. The current Catechism is structurally different than the one I grew up with but the basic content is the same. So I would just have to say that the only difference in Catechisms in the last 150 years or so is the structure, not the content.
There is a new Catechism geared to young people. But it is based on the bigger Catechism. Both are correct, just a different approach.
The difference between the Philosophy of St Thomas or St Augustine and the Catechism is that one does not have to believe all of what St Thomas said is true, though much, perhaps most of it is true. We only have to believe it if we are absolutely certain that what he taught is true and as long as it does not contradict what the Catechism teaches or what the Church teaches elsewhere. But we do have to believe what the Catechism teaches to be Catholics in good standing.
St. Teresa and St. Thomas were both great Saints and both Doctors of the Church. I’m not exactly sure how to explain the difference except I think St Teresa would be regarded more as a Doctor of Spirituality and Thomas as a Doctor of Philosophy.
