Here are verses where something similar to my understanding of Ephesians 2:8 is presented.
What verses display "pisteos" being used in a subjective genitive phrase?
Romans 3:3 What then? If some did not believe, does their unbelief nullify
God's faithfulness?
Romans 3:22 namely, the righteousness of God through
Jesus Christ's faithfulness for all who believe. For there is no distinction,
Romans 3:26 This was also to demonstrate his righteousness in the present time, so that he would be just and the justifier of the one who lives because of
Jesus' faithfulness.
Galatians 2:16 yet we know that no one is justified by the works of the law but by
Jesus Christ's faithfulness. And we have come to believe in Christ Jesus, so that we may be justified by
Christ's faithfulness and not by the works of the law, because by the works of the law no one will be justified.
Galatians 2:20 I have been crucified with Christ, and it is no longer I who live, but Christ lives in me. So the life I now live in the body, I live because of the
Son of God's faithfulness, who loved me and gave himself for me.
Galatians 3:22 But the scripture imprisoned everything and everyone under sin so that the promise could be given - because of
Jesus Christ's faithfulness - to those who believe.
Ephesians 3:12 in whom we have boldness and confident access to God because of
Christ's faithfulness.
Philippians 3:9 and be found in him, not because I have my own righteousness derived from the law, but because I have the righteousness that comes by way of
Christ's faithfulness - a righteousness from God that is in fact based on
Christ's faithfulness.