My understanding based on what I hear from friends in the industry is that this is definitely not true, especially earlier on in a pilot's career. If one plays their cards right, you can make a good deal more as a 'cargo dog' pilot when you're young, compared to working for a regional or non-major airline, which is where most younger passenger pilots begin their careers. However, the disparity in pay can be more pronounced later on, as senior pilots at the major airlines can in many cases make much more income, or have a much better work-life balance.
Did a little googling as I was curious, and sure enough, wow Fedex pilots are well paid. Also, I know that while Fedex pilots typically fly overnight, its only a few times a week and they have the ability to be around for daytime events. One of my lacrosse coaches in high school was a Fedex pilot, and he seems to do quite well while being available to arrange his schedule. All-caps emphasis mine below, Fedex is dramatically higher.
"According to Memphis newspaper The Commercial Appeal, pilots flying for FedEx earn closer to $234,000 a year ON AVERAGE -- 90% more, to carry boxes from Point A to Point B, than the folks flying actual human passengers make.
https://www.fool.com/investing/general/2015/09/05/pilots-are...
"Salaries at Delta Air Lines Inc range from an average of $42,495 to $144,385 a year. Delta Air Lines Inc employees with the job title Airline Captain make the most with an average annual salary of $188,104
