I think there's a missing element from the description of "strong favorable signals must be costly". In fact, they must be costly TO FAKE. They can be cheap when honest.
I think you have to accept the truth of your observations (it's not tautological if it requires evidence to support, and you happen to have that evidence). A whole lot of humans have difficulty with impulse control, and with subverting their natural reactions and desires in order to appear friendlier and more vulnerable than their inside view of themselves supports.
This post doesn't convince me away from the "tautological" objection mentioned at the end.
Caplan is presenting a contrarian position: "Standard signaling models are incorrect. The true cost of making friends is astronomically lower than what most people think it is." It's an intriguing take, but what are those actual and perceived costs?
To me, it's borderline ridiculous to simplify the costs down to "impulse control." Making friends is often difficult, complicated, and at times genuinely risky. It takes so much more effort and commitment than simply saying hello with a smile. Even for the "sincerely friendly" people who have good social intuitions, there's clearly an opportunity cost to having friends.
I'd be interested in an analysis of the perceived vs actual costs of friendship, but I don't see any of that explored in detail here. Even the core claim that "people are impulsive" doesn't seem particularly well supported.
Note that in the current world, the value of certain skills has grown so large that having friends is not cheap. Your time has become worth north of $100 an hour, if you are in the USA and if you can get into a tech job etc. Sometimes a LOT more than that. Every hour you waste on a friend is an hour you could be studying, tinkering on a personal project, or working.
Ironically just spending money on signaling becomes cheap. That leased Tesla or bmw costs you barely anything per month in terms of hours invested. Your fancy watch is the same story. Hence why you see so many bay area bros all looking the same.
By Bryan Caplan, Economics professor at George Mason University, posted on his blog Bet on It on March 16th 2022. This is the original source of the legendary quote.