As compelling as this view is, I suggest that it over-states the Pauline and Protestant understanding of grace. Yes, Paul says we cannot be justified by our own works, and he contrasts justification by works with justification by faith in Christ (e.g., Gal. 2:16; Rom. 4:4–5). But he does, in fact, say in many places we are justified by our faith, and he never contrasts our faith with the work of Christ. Instead, Paul can say in the same breath that we are both "justified by [our] faith" (Rom. 5:1) and "justified by his blood" (Rom. 5:9).https://www.crossway.org/articles/faith-in-christ-vs-the-faithfulness-of-christ/
Grammatically, there are other places where the genitive refers to Christ as the object.
In Philippians 3:8, Jesus Christ is described as the object of knowledge. In 1 Thessalonians, he is described as the object of hope. In both these cases, it is clear from the context that Paul is not talking about Christ's knowledge or Christ's hope. There is no grammatical reason why the same can't be true of pistis christou.https://www.thegospelcoalition.org/blogs/trevin-wax/faith-in-christ-or-faithfulness-of-christ/