Not quite true. Luke was a Gentile writing to Greek Christians.
Matt 15:24,
But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
Does Luke being a Gentile supersede this clear declaration by Jesus?
Why? Doctrine was, in the beginning, based upon the Apostles’ teaching, since there were not yet any Christian scriptures. By basing doctrine on the epistles, we miss out on Jesus’ teaching.
Are you suggesting that the epistles were somehow not the same as the Apostle's teaching?
Where would one find this "Apostle's teaching" anyway? Apparently it's not in the scriptures.
The gospels were largely written after the epistles. The gospels reflect later thinking than Paul.
If you want to take your doctrine from the gospels, keep this in mind;
Matt 5:28-29,
28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
29 And if thy right eye offend thee, pluck it out, and cast [it] from thee: for it is profitable for thee that one of thy members should perish, and not [that] thy whole body should be cast into hell.
If we all actually did that, we'd see churches full of blind people. Also people missing at least one hand,
Matt 5:30,
And if thy right hand offend thee, cut it off, and cast [it] from thee: for it is profitable for thee that one of thy members should perish, and not [that] thy whole body should be cast into hell.
But I suppose nobody wants to follow Jesus that much!