I think it is important to point out that FRC is not a competition about it is not about which mentor team can build a better bot. The mission statement of FIRST is: "Our mission is to show students of every age that science, technology, and problem-solving are not only fun and rewarding, but are proven paths to successful careers and a bright future for us all." -
www.usfirst.org
Keyword: students
Not only that, but this is a competition for High School students. If mentors do a majority of the building, then what is the point of the competition? One could hire NASA engineers to build them a better robot and they would crush the group of high school kids that built their bot themselves. While it is important for Mentors to help, they SHOULD only be there for teaching purposes, no matter the skill of your team.