if you are trying to ask me a leading question and then jump on me after I answer to play- gotcha-
Ok, you caught me. That is what I was trying to do, but not as a trick, merely to "cut you off at the pass" so to speak and try to anticipate where you're going with it.
It was sufficient for Jesus to affirm it as a correct understanding of Him as the foundation upon which the church would be built and stand against the gates of hell.
But I think this completely fits a Trinitarian theology rather than speaks against it. Because of that little word, Christ, Messiah, Meshiach, the anointed. Let's go to the OT and see what the role of the Messiah is, and it fits a Trinitarian soteriology. Can you honestly say that you think Peter fully understood everything "Christ" meant there? We are so used to throwing the term Christ around as if it were hardly anything at all. "You are the Christ," would then be defined by the rest of the revelation of Scripture about what the Christ came to do and who the Christ is. It's a segue, as it were, to a broader revelation, and not a catch-all "rock" in and of itself.
do you think one does not need to affirm the Trinity to be saved either?
No, for a couple reasons. The Bible indicates we don't need "all" truth to be saved, nor even necessarily just "data" about truth, but a real regeneration. Also, even the disciples could grow in their understanding of God and truth, after they were already described as "saved" by the working of Christ. You can have a very, very simple understanding of Jesus as sent by God for salvation, and the heart of that is salvation by faith through grace in his offering and resurrection. The Trinity is just a fuller and more complete picture of Biblical revelation. (Do you need proper eschatology to be saved? Of course not... do you need to understand predestination to be saved? Never. We believe as we search and pray God's Spirit will gradually lead us into more truth...)