Regarding the point you make about 20% of the people doing 80% of the work, that's half true. I find that 20% of the people do 80% of the work, but for any given period of time it's not always the same 20% of the people. One iteration might have a couple of back-end devs doing most of the stories, and the next iteration will find those two doing less while 80% of the stories are done by a DBA and a UX researcher. I've never had a team where one person consistently does most of the work. If that was the case I would be concerned about the make up of the team - clearly I'd need more people who do the sort of work that person is doing and less of the other team members.
Obviously my experience is not universal, so your experience may be very different.
Give me a team of superstars and we'll deliver a half-finished framework for solving the general class of CRUD problems one could have, along with a bad implementation of a gherkin dialect.