Jesus Christ is the pillar and foundation of Truth and not the Church. If you are speaking of the universal church it is built on Christ and that is where it it derives it’s truth. If you are talking about the Roman sect very little of the truth remains in it. That is one of the problems with the catholic church. it keeps trying to build on anything but Christ. (Peter, Mary, and according to your tagline even the church itself are described as what the catholic church is built on. There is only one cornerstone and foundation worthy of building on and that is Jesus Christ and Him crucified.
I don't blame you for it, I just find it unpersuasive. Jesus is the TRUTH. He is not called by St. Paul the "pillar and foundation" of the truth, because He is the TRUTH. A pillar and foundation (or one could say, pedestal) of the Truth is that which upholds the truth.
Paul is saying ere that the Church (pedestal) upholds the Truth (Christ.)
It's hard to see why a Christian would quibble with Paul on that point.