> enough to make the utility loss worth it for most people
The author of the essay (I believe you are the author) says "don't double major" and that a double major is "a very suboptimal strategy."
You now write that it's not worthwhile "for most people", which implies that it is the optimal strategy for some people.
These two statements are not in accordance. Which is it: a bad strategy for everyone, or good strategy for only a few?
That you think it is never worth the effort therefore more likely means that you have incomplete information about the utility of a double major, and not that the myriad of people with double majors have made the wrong decision. I actually think it's because you don't understand your own mental model.
Many fewer people double major than get a single major. In a utility maximization framework, this indicates that double majoring is sometimes worth the extra effort. In your statement here, you believe the additional utility is an order of magnitude less than getting a degree in the first place. In which case, if the additional effort is also an order of magnitude less (assuming linear scaling) then it's worthwhile.
Assuming 120-130 credit hours to graduates implies 12 hours for a second degree is an acceptable amount of additional work. You mentioned elsewhere people who were "three boring classes" away from a double major. That's 9 credit hours, which means it's likely a reasonable decision under the model you just proposed.
Your statements don't seem to be in agreement with your model. Can you explain how you used that model to come to a different conclusion?