We are not saying that the books in Luther’s OT canon are not inspired, just that the canon was truncated by him
Actually Luther did not truncate them, but that was done by Jews. Luther included those books in an appendix, and that was later dropped in the 1800's. But the Bible is not the gospel. The gospel is simply the good news of Christ. And I think we can all agree on what the good new of Christ means to us all.