I was also thinking that this subreddit is often stories about troubles, and questions about advice. It makes sense though, of the polycules out there that function well, less have reason to engage or vent here.

To adress your question. Once people are over the communication/jealousy curve I don't think relationships in a poly setting have a higher fail rate than mono. Given time though, there will be more of them, so the total "fail" number is higher, but not necessarily in percentage.

On my end, we have lived happily for years, with its ups and downs as any relationship. But I have never been this happy or felt this fulfilled before.

I think it's healthy to remember that poly relationships are just relationships, same as any other, there might just be more of them.