Either way the takeaway here would seem to be that there is no issur of profiting from a goy's mistake but you're gonna lose it all in the end anyway. And additionally, if you realize after the fact that you profited from a goy's mistake there's no chiyuv to return it, but if you do you'll see brocha in the end.
I disagree with your "takeaway". It is clearly a machlokes rishonim with different achronim saying different things. Hence the necessity to ask your Rav. In addition, even the rishonim who are matir, never permitted the other issurim that can be involved, namely Chilul Hashem and Being Meshaker. (All the poskim that I have ever seen permitting this were very clear that if there's a chance Chillul Hashem that is remains assur, with many of them then going on a rampage about how chamur the issur of chilul Hashem is)
If you want to be more informed on the topic, pick up a copy of "Halachos of other people's money" by Rabbi Bodner, where he goes through all of these issues very clearly. (though mostly in the footnotes, so if you can't read Hebrew you'll always come out stringent)
As Daniel said, I never said anything was assur or mutar, (though I might if you asked me), just bringing up the need to ask.
(I personally have already asked many shaylos from things that came up on this site and was told that some are mutar some are assur and sometimes I was told mutar but don't do it. I.e. a yid shouldn't do that even if technically it's permitted which I guess you could call lifnim mishuras hadin)
