John 17:3 isn't meant to explain away John 17:5. It isn't meant to explain away anything. You are trying to explain away John 17:3 using John 17:5, I have seen you pull that stunt many times. You don't believe the Father is the only true God so you search everywhere for reasons to attempt to justify that belief. Why do you not believe the Father is the only true God and also believe John 17:5 in a way consistent with that?
Your version of John 1:18 says "No one has ever seen God" then after that it says of Jesus "the only God" and later everyone saw Jesus. Yes, it's a contradiction. No one has seen the Father, but Jesus is a human whom everyone has seen. Jesus isn't the invisible God that no one can see.
Look, Jesus isn't the invisible God again:
Colossians 1
15Who is
the image of the invisible God, the firstborn of every creature:
1 Timothy 1
17Now
to the King eternal, immortal, and invisible, the only God, be honor and glory forever and ever. Amen.
Ephesians 4:6 debunkes the trinity. It says the one God is the Father and that He is over all. That tears to shreds the idea of a coequal trinity if there is only one God, the Father, who is over them.
Ephesians 4
6one God and Father of all, who is over all and through all and in all.