You said, "'We' is the plural of Majesty, and not the Christian plural of trinity" This is your misconception. The trinity is the majesty and the oneness of God. It is perfect monotheism.
As for the Quran, you didn't mention why Hafsa's copy was destroyed after Uthman used the help of text from her copy. Wouldn't this leave an element of doubt as to why it was found necessary to destroy her copy when Uthman used it to recompile the Quran? We cannot check her copy to see if it all lines up with Uthman's compilation, because of its destruction. This proves to me that you cannot prove unequivocally the perfect preservation of the Quran. You may be convinced, but I can see this element of doubt unless you can explain why Marwa destroyed her copy after Uthman used it to standardize the Quran after Islam's prophet's death and after his wife's death. You need to explain this; otherwise there is a whole in your explanation. Finally, you didn't address who gave the divine mandate to put the Quran to writing when it means recite and not write! God promised the Scripture that came before was established secure in heaven before the Quran; so, why does the Quran contradict the Scripture God promised was established forever before Islam's prophet's birth...
These questions need to be addressed before you can claim proof of the preservation of the Quran