This assumes that representing people requires skills, experience, and expertise that can not be obtained elsewhere and can not be provided by advisers

That’s correct. It can’t be. New Representatives basically get nothing done. It takes them the two years they have to learn the ropes before they have to start fund raising for their next election. Federal Office is like Professional Sports. How often does someone just walk into it with no prior experience and succeed? It’s not just about representing. It’s about knowing how to negotiate and convince other representatives to care about what your constituents want. If Advisers are doing all the work, why don’t they just run? You know who has all the time and money to “advise” candidates? Lobbyists.