I agree that John and Mark are based on eye-witness testimony. Luke & Matthew copy Mark so to that extent we can say they are based on eye-witness testimony, but they themselves were not eye-witnesses they had to rely on two copied texts and some other sources which we do not know. I don't know why you believe Luke has 'perfect understanding', simply because he claims it? If I claim perfect understanding would you believe me? Of course not.
I also agree the Two eye-witness gospels are key to understanding Jesus and God. That is why we need to study them and understand the context in which they were created - it will greatly extend our understanding of the message they contain.
“Luke & Matthew copy Mark so to that extent we can say they are based on eye-witness testimony, but they themselves were not eye-witnesses”
see Luke explains this part
“Forasmuch as many have taken in hand to
set forth in order a declaration of those things which are most surely believed among us, even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word;
( this is why we have the gospels they are what we believe )
it seemed good to
me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus,
that thou mightest know the certainty of those things, wherein thou hast been instructed.”
Luke 1:1-4
Luke is writing an orderly account of things the apostles established and also things he himself knew from the very beginning. So if we take Luke as credible it’s based on his own and others eye witness accounts
mark , he also would be setting an orderly account of things everyone had saw and experienced being present both he and Luke in the early church and both mark and Luke were beneficial participants and fellow workers in Paul’s gentile ministry
“For
I am now ready to be offered, and the
time of my departure is at hand. I have fought a good fight,
I have finished my course, I have kept the faith: henceforth there is laid up for me a crown of righteousness, which the Lord, the righteous judge, shall give me at that day: and not to me only, but unto all them also that love his appearing.
Do thy diligence to come shortly unto me: Only
Luke is with me. Take
Mark, and bring him with thee: for he is profitable to me for the ministry.”
2 Timothy 4:6-9, 11 KJV
Luke isn’t based on his own witness like acts , he says it’s based on his own witness and understanding of things and the things as the apostles had witnessed also to the believers in the region
see in reality they were always preaching the things we have now written down in the four gospels the epistles are letters sent to help correct things circles didn’t grasp and help
Offer more understanding of the four gospels
definately they aren’t personal witness accounts in Luke only or mark I agree they are definately witness accounts though like this , this is based on eye witness accounts
“ Jesus taketh with him
Peter, and James, and John, and leadeth them up into an
high mountain apart by themselves: and
he was transfigured before them.
And his
raiment became shining, exceeding white as snow; so as no fuller on earth can white them.
And there appeared unto them Elijah with Moses: and they were talking with Jesus.
And
Peter answered and said to Jesus, Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one for Moses, and one for Elias. For
he wist not what to say; for they were sore afraid. And there was a cloud that overshadowed them: and a voice came out of the cloud, saying, This is my beloved Son: hear him. And suddenly, when they had looked round about, they saw no man any more, save Jesus only with themselves. And as they came down from the mountain, he charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead. And they kept that saying with themselves, questioning one with another what the rising from the dead should mean. And they asked him, saying, Why say the scribes that Elias must first come? And he answered and told them, Elias verily cometh first, and restoreth all things; and how it is written of the Son of man, that he must suffer many things, and be set at nought. But I say unto you, That Elias is indeed come, and they have done unto him whatsoever they listed, as it is written of him.”
Mark 9:2-13 KJV
Only someone there would know the details of what was said and asked and what Jesus replied
and Peter answered and said to Jesus, ( he knows who spoke to who and what was said )
Master, it is good for us to be here: and let us make three tabernacles; one for thee, and one for Moses, and one for Elias.
For
he wist not what to say; for they were sore afraid.
( he knows how they felt and why peter said it
)
what I mean is they are all this way coming from eye witness accounts even mark and Luke they are attempts like Luke says to present an orderly account of Jesus life after his baptism walking among mankind his ministry and teachings , miracles , death and suffering , resurrection and even his ascention is all based on eye witness accounts no matter if Matthew mark or Luke wrote or even John
his of Course is much more intimate and spiritual as the others are more of a record of what happened and what was said