2 Peter 1
16 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.
17 For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased.
18 And this voice which came from heaven we heard, when we were with him in the holy mount.
The Transfiguration was not a "coming". Jesus was already here.
Moreover, in Matt 16:27, it says Jesus comes with angels, and rewards each person with gifts.
None of those things happened at the Transfiguration.
Lastly, the Transfiguration happened 6 days after Jesus said "some of you will not taste death....". That implies that most of them would be dead when the coming took place.