This proves what? Some early papyri is missing the end of Matthew. Later editions contain the end. Do you believe that every copy of Matthew ever written is still intact?
As for the Trinity, it is true that Jews believed that God was one. Christians believe that God is three in one. John tells us about “In the beginning, the Word...” Jesus said that he would send another, a great counselor. I’m not going to go through a complete exegesis because it would be a waste of time. If you don’t believe, then don’t believe. I won’t try to evangelize to you. I have no interest in doing that for you. You are happy with your spaghetti monster and I am happy with Jesus.
My favorite bit of evidence is that one church father supported the baptism phrase "ITNOTFSAHS" but didn't use Matthew 28 to justify it, rather
http://www.godglorified.com/Ending.pdf
"First, as we suggested above, there is no early manuscript evidence of Matthew 28:19 in its longer form. "
"Second, the standard Greek text utilized today argues for or against the inclusion of specific phrases and words based upon attestation by the church fathers. (UBS) 4th edition of their Greek New Testament, (GNT) they reference 116 different Greek, and 74 Latin Church Fathers. One of the most prominent Greek Church Fathers is Eusebius of Caesarea. He is quoted or referenced 189 times in the UBS’s GNT. Eusebius is cited 116 times in the Gospels alone. The single Gospel he is cited most is Matthew, with 47 citations. But in spite of the fact that within the writings of Eusebius there is a form of Matthew 28:19 significantly different from the traditional form, it is ironic to me that Eusebius is not cited at this verse.
One may well suspect that there is a doctrinal motivation to prevent this allimportant text from being considered “disputed.” Elsewhere I argue that hermeneutically, Matthew 28:19 as it stands in its immediate context must point to a single name, the name of Jesus as being the correct hermeneutical interpretation for this passage.20 But if in fact the passage is spurious, if in fact it should be possibly disallowed, then the text should be approached tentatively for doctrinal support of Trinitarian theology. We will now look at how Eusebius cited this verse most frequently in his writings. We will provide it in Scriptural context so one may get the true feel for how it flows.
All power is given unto me in heaven and earth.
Go and make all nations disciples in my name,
Teaching them to observe all that I have commanded you.
And behold, I am with you all the days till the consummation of the aeon.
“Scribes occasionally altered words of their sacred texts to make them more patently orthodox and to prevent their misuse by Christians who espouse aberrant views.”
And without quotes, I assert based on the available evidence such altering occured even in the 4th Century in response to the Trinitarian controversy.