Jesus life was the example which everything else in our faith is based, so it is useless to say that what is said later is more important.
It is true that, in the tradition of the Church, there is a "hierarchy" within Scripture. In that sense, you can say that the Gospels are "higher" than the Epistles. But this does not mean that we choose the Gospel when there seems to be a conflict with an Epistle. That's not what the "hierarchy" is intended to do because we also believe that Scripture is to be interpreted in light of the other Scriptures. If we're seeing a conflict between two passages, the solution is not to throw out the "lower" passage, absolutely not. We must interpret Scripture with Scripture and with the entirety of ecclesiastical tradition. If we throw out anything, it is our erroneous thinking.
You are right that Jesus' life--his person--is the source from which our faith flows. But it does not follow from this that the Gospels overrule the Epistles. The earliest Gospel was still written after the earliest Epistle, and both are later than the oral preaching of the apostles. We know Christ ultimately within and through the Church. Ss Luke and Cleopas walked with the risen Christ, but only "knew" him and recognised him in the breaking open of the Scriptures and the Eucharist. After this, he disappeared, but he remained with them in the Eucharist. Similarly, Jesus extraordinarily intervenes in the life of Saul of Tarsus, but he still needs Baptism and Communion within the Church in order to understand what was revealed to him (and St Paul definitely seems to regard at least some of his letters as "Gospel" and "Scripture" as we would understand them, and not just in terms of kerygma).
The primacy of Jesus doesn't give us licence to nullify some Scripture with other Scripture, but points to the necessity of being incorporated into his Body in order to understand any and all of it. And from within the Body, we do not limit ourselves to what was said before, but also how it was interpreted later, because wherever in time a writing pops up, it is still popping up in one and the same Church.
And you can be weak in the eyes of the world without having weak arguments--in fact, we must combine humility with truth. If the apostles preferred weak arguments to accompany their humility, I'd still be worshiping idols and so would you. So let's avoid false humility.