The gospels were not written as Jesus spoke. They were written at some point many years later by people who recalled what He spoke (or recalled what they heard that He spoke)--by inspiration of the Holy Spirit.
That same Holy Spirit inspired Paul to write what the Holy Spirit wanted him to write.
It doesn't make sense to think that the Holy Spirit who inspired one set of unknown writers was less reliable than the Holy Spirit who inspired Paul.
Of course the Gospels were not written as Jesus spoke. Again, I never meant to imply they were.
However, they did involve participation of witnesses.
Paul alone among the Apostles (I'm not saying he wasn't one or shouldn't be) "came late" to the game, as it were. Still, that matters not much as he did "meet Christ" and was directly taught of the Holy Spirit.
I'm not sure how you view the inspiration of the Holy Spirit. The epistles of course had that inspiration, but I don't consider it as something like automatic writing or being directly dictated. The voice and inclinations of the writer show through.
For these reasons - I (and many others) would say that the recalled words of Christ Himself by witnesses and brought to remembrance of the Holy Spirit - have some preeminence over the words penned by those whom the Holy Spirit has taught and is bringing principles to mind. All are true. All are inspired. But some parts of Scripture are more important (to many of us). And that's all I'm saying. If you don't agree, that's fine. I'm a little surprised so much back and forth is necessary over this.
But for example, the Beatitudes and the Lord's Prayer - are far more significant to us (Orthodox) than many other randomly chosen passages. The Gospels are more significant than the epistles. The New Testament is more significant than the Old. And so on.
If someone else sees it differently, that's fine. But I don't know anyone who in practice would rate, say, the OT genealogies on par with the Beatitudes in terms of importance.
And I'm only saying that Christ's own words intended to teach us, remembered by witnesses, brought to mind by the Holy Spirit - are of generally of more importance that letters written by the Apostles (under the inspiration of the Holy Spirit) sent to the various particular Churches they had established in order to encourage, correct, or instruct those particular communities (though being true for a congregation then are likewise true for a congregation today).