I can't think of a counterargument to the aphorism that good times produce weak men. Nobody knows the value of anything and counterproductive things are prioritised.
Sure, you could say that the counterexamples are just distributed away from politics, but that feels like haggling with the premise of the argument instead of disproving it.
It seems to me that the relatively good times of the late 19th Century in both Europe and America left a lot of young men spoiling for a challenge. In the US this probably contributed to the Spanish-American War. Theodore Roosevelt had questionable judgment, but I don't think he was weak.
Sure, you could say that the counterexamples are just distributed away from politics, but that feels like haggling with the premise of the argument instead of disproving it.