That may well be "some of the reasoning" behind the max seat configuration element of the definition. But, as always, the solution to one problem almost invariably creates at least one other problem. The plain words of the current definition of a flight that is 'cost-sharing' do not set a POB limit on 'cost-sharing' flights.
What's to stop a "backyard skydiving" "crowd" from stripping a C206 and cramming 8 skydivers into it?