The foundation (Jesus Christ) isn’t - but the church is sure filled with sin-prone and fallible people. And of course extending back through history with the Hebrews as well. I love that both lineages of Jesus are filled with people with a sordid history. I think those lineages go out of their way to include them (the women for example, which typically were not included in a lineage.)
It doesn’t matter to me what a catholic wants to believe when it comes to Peter and the Pope or whatever. And I won’t bash them for it. There is a day coming when all Christians will need to set aside these differences, big and small, to join together against the muslims.
But for me, I agree that what IS building the Christian church is the revelation and inspiration of the Holy Spirit. Take for example the recent stories of muslims having dreams of Jesus Christ, and only understanding them after a Christian has witnessed to them. And then they convert! (This just happened a little while ago to one of our pastors when he was visiting a school we have set up in Rwanda.)
That stories of Muslim conversions are absolutely wonderful! I pray they will come to Jesus in ever greater numbers. I also pray blessings on your pastor and the school in Rwanda; may God guard and prosper them.