One of the benefits to the mentor is actually the impetus to stay out ahead in the area of expertise. This mentor will be motivated by advancing the discipline, and a mutually useful network can be built and perpetuated. Make those 20 percent your network and be creative. Don't ever write a boring memo, don't ever write a boring thank you note. Don't ever make a boring phone call.
People buy from other people because of chemistry and likeability.
That's not going to change in the next 50 years. Tell me how you're going to do that without a network. Talent alone will not save you in today's economy. More training and education alone won't save you. Seeking out and learning from mentors, as well as developing advisory networks takes time, of which most young lawyers have little to spare.