I've been selling health insurance to older people since 1963. That's 3 years before there was even a federal Medicare Program. Your summation of Medicare Advantage was highly accurate and well presented. Others should bookmark this thread and especially your reply as a reference!!!
The only thing you may have left out is that the more remote a county is within a state, the less likely an insurer is to offer one of these plans, especially if it's an HMO instead of a PPO. (due mainly to lack of member doctor providers also approved by Medicare)
Thanks!