Only 35 percent of brokers were hired from outside the insurance industry (including from college), the research found.

Especially troubling, Reagan Consulting noted, 55 percent to 60 percent of firms are "under-hiring," meaning they are not hiring enough new brokers to achieve their growth objectives or allow them to successfully perpetuate their business. Worsening things more, the firm said, is the fact that "free agents," who move from agency to agency, "were by far the largest category of producer hires," accounting for 55 percent of new hires over the past five years.

Still, a wide discrepancy was found in the trends: the top 25 percent of firms had a hiring success rate of 84 percent compared to a 22 percent success rate for the bottom 25 percent of firms.

For its survey, the firm gathered baseline data from 4,641 brokers from 562 firms and conducted a follow-up survey with 112 firms that hired 1,505 new employees over the past five years.

Reagan Consulting's findings mirror other concerning findings about the broker business from Aflac's Report for Brokers, released earlier this year. Aflac found that about half of brokers said they're considering leaving the broker biz and 67 percent of brokers say they've seen many of their peers exit the industry in the past year.

"Due to uncertainty about the evolving health care landscape, brokers found themselves at a crossroads of either redefining their role in the industry or exiting it entirely," Aflac said in June.