It's not so much that Christianity is the source of justice, hard work, and loving children as that Christianity claims to be the source of these things.
And, since Christianity is inextricable from European imperialism, those "values" were used to claim moral superiority to other cultures, in order to justify the pillage. Because other cultures clearly don't care about justice or work or children, right? Right.
Your inversion can itself be inverted. The success of Christianity is arguably derived from European political power - first the Romans, and then the colonialist explosion across the globe that started with Spain in the New World (closely followed by England, Holland, and France), which was a result of technological advantages, not moral ones. Without colonialism, Christianity would be merely an also-ran religion confined to a European backwater.
And, since Christianity is inextricable from European imperialism, those "values" were used to claim moral superiority to other cultures, in order to justify the pillage. Because other cultures clearly don't care about justice or work or children, right? Right.
Your inversion can itself be inverted. The success of Christianity is arguably derived from European political power - first the Romans, and then the colonialist explosion across the globe that started with Spain in the New World (closely followed by England, Holland, and France), which was a result of technological advantages, not moral ones. Without colonialism, Christianity would be merely an also-ran religion confined to a European backwater.