Your understanding is considerably worthy.
In my estimation, I can't tell if it was a vision placed in each of the three disciples head, or that it was a reality for their mortal eyes.
Either way would do for me, because the fact is none of them were told in the moment of who the entities were, except that in advance Jesus said that they would see heaven open and angels. I'm going with what Jesus said they would see, whether literally or by a vision. Thanks for sharing that understanding.
Edit: the other question that grabs me is, why the need for Jesus to take them "up into a high mountain apart" for them to see it. According to the power of God, visions can be given at any time, in a person's quiet time.
But, if it was a literal reality, I can understand why Jesus didn't want others to literally see it.
Earburner I was fascinated, when I was doing my verse by verse studies.
So I praise God for the information received,
Here is where we can see it was indeed a vision from youngs literal,
Matthew 17:9
And as they are coming down from the mount, Jesus charged them, saying, 'Say to no one the vision, till the Son of Man out of the dead may rise.'