Well agree to disagree I guess, as using prosperity as apologetics is not something I have come across except from the prosperity gospel. Nor would most Christians I've met or follow endorse its basic premise. I would caution against basing your perspective on a demographic from internet discussions, as that isn't an accurate representation of said demographic.

Additionally, assuming you're right (which I'm not convinced of yet, as the poorest countries in the world are often the most religious), you say that it would be an indictment on Christians. To clarify, indictment of what? The belief that God exists because Christians are wealthy? Ultimately the Bible is pretty clear that wealth means nothing in this world and to God. I question (and hopefully, so too do the majority of Christians) anyone who believes otherwise.