I would just contest the notion that "most great agents don't want to undersell their own industry." Not only does that kind of thinking assumes that compensation and customer service are tightly coupled -- even though "getting more for less" is one of the best working definitions of innovation -- it does a real disservice to the folks who have enough vision to work at a place like Redfin.
What is your definition of "great?" If you're referring to actual outcomes, check out Redfin's agent reviews -- the overall NPS rating blows any other brokerage out of the water, and is comparable to some of the best known consumer brands in the world. Equity compensation, automation of mundane tasks, a real team mentality when the agent next to you is a fellow employed colleague, not an independent contractor who happens to share a split with the same franchise -- these are all reasons a "great" agent might want to work at a place like Redfin.
Finally, many agents realize that the status quo (6% fees and asymmetric information) won't exist forever; it's all the NAR can talk about these days. The most far-sighted among them would rather work at an institution that is embracing and driving change, not resisting it.
All of this also assumes your axiom that Redfin agents are compensated less than traditional agents. Without going into too many details, I can say the opposite is true in most cases.
Disclosure: I work at Redfin.