I can see where your friend is coming from about being drafted sooner in the NFL but much of the research points to lower lifetime earnings for those who are redshirted. For example, would he have had to retire a year earlier because he would have been too old to play and would have missed an entire year of earnings.
"And finally, parents should bear in mind that redshirting can even have an effect on their child’s economic future. Starting school at age 6 instead of age 5 means heading off to college at age 19 instead of age 18. (Perhaps spending an extra year with a teenager in the house is another cost to consider!) Then the student graduates from college and enters the workforce at age 23 instead of age 22. The redshirted individual will ultimately spend one less year in the labor force and forgo the returns of an extra year of experience throughout his working life. Assuming that, as research seems to indicate, being redshirted has no net long-term impacts on skill level, we can estimate the cost of losing that year in the labor force for a college-educated male who retires at age 67. Over the course of the worker’s career, working full time and year-round, he can expect to earn $80,000 less."
http://educationnext.org/is-your-child-ready-kindergarten-redshirting-may-do-more-harm-than-good/