This seems like a reasonable hypothesis, but I don't perceive a clear signal that indicates that projects which use monads or pure FP are more successful than t

This seems like a reasonable hypothesis, but I don't perceive a clear signal that indicates that projects which use monads or pure FP are more successful than their counterparts. I think your hypothesis actually jives with mine and with my observation from the previous sentence--that monads and functional purity could help, but if the language neglects things like documentation, high quality libraries, and tooling to productionise and operationalize your code, then it's a non-starter.