Good morning, Daniel Marsh,
What an interesting picture you included with your post. Actually, yours was the first picture I had seen in a post - just did not realize that such an approach was possible.
In my judgment, the use of Eph 2:20 does not really seem to address the issue.
So then you are no longer strangers and sojourners, but you are fellow citizens with the holy ones and members of the household of God, built upon the foundation of the apostles and prophets, with Christ Jesus himself as the capstone.(Eph 2:19-20)
The thrust of the Chapter in Ephesians is to show how both Jew and Gentile - both following Christ have been joined into one community with peace. (Hopefully, my one sentence summary did not do too much violence to the Scripture.)
Peter is not singled out in your reference. Actually, as you can see: the reference is including all of those who are part of God’s Plan for our Salvation and summarized as, “…apostles and prophets…”.
Actually, I think anyone would be hard pressed to identify Peter as just “one of the boys” when the entiere New Testament is identified. Even the trio of Peter, James and John - the group that was most privledged in Jesus’ company, still acknowledges Peter’s leadership. Then there’s that annoying, “keys to the Kingdom” quote (Matt 16 ) and “Do you love me more then these?..feed my sheep” (John 21 ).
As I see it, one of the difficulties of using non-Scriptural sources to refute Scriptural sources is that one is always coming up a bit shy of the mark. While the Shepherd is of interest, Christ only addressed Himself as the cornerstone (Matt 21:42) - and Christ then made Peter (the Rock) as the foundation (Matt 16:18). Unless I have missed something here - this is the only pun Christ told (how is that for Divine comedy?

)
We simply see Peter as one of those rocks or stones just like each of the prophets who came before the apostles themselves are part of the foundation stones.
While seeing all of us - all of God’s People - as part of the ‘rocks or stones’ in the building of God’s Kingdom is certainly a good approach. To cover over the one Apostle that was simply singled out by Christ Himself to be the leader of the Church - is to miss the point of the New Testament message. That messaage is:
Christ has prepared our Salvation in the manner He has selected.
Christ actually chose to die on the Cross.
Christ actually chose to build a Church on a very weak human being - who would be lead by the Holy Spirit.
Christ actually chose to have His Church carry on when He gave the Great Commission - it did not end with the Original Twelve.
Christ actually chose that each of us would in some way be dependent on each other - through Christ and His Church - to come to Him.
Christ actually chose Peter - and his successors - and they represent Our Lord’s on-going Plan of Salvation for each of us.
Arguing otherwise, really does pit the traditions of men aginst the Will of God.
Best wishes