Medicare Advantage is shit insurance - and the 3 minute infomercials are for Medicare Advantage plans - not Medigap. (I've **never** seen a Medigap advertisement -- or received mailings during the enrollment period to entice me to buy a Medigap policy.)
My health care, with a Medigap policy, is more comprehensive, cheaper, with fewer barriers to care than I've ever had in my life. (And I've had insurance coverage for the past 52 years).
My total cost for non-pharmaceutical medical expenses this year are $4338 (premiums + out of pocket expenses) - no matter how expensive my care actually is. Ballpark, my pharmaceutical expenses add on $2-300 (premiums + drugs). For my spouse (one of those expensive pharmaceutical creatures) will add up to $2100 to her annual cost (we haven't refigured since she dropped one expensive medication in favor of one which is capped at $35/month). I can go to 98.8% of the non-pediatric doctors in the country (only 1.2% of non-pediatric doctors have opted out of Medicare). I don't need a referral to see any of them. I don't have to wait for pre-approval of expensive things like MRI, etc. (Only a handful of primarily cosmetic procedures require pre-approval, except for the 17 (IIRC) added this year in the state in which I live.) If I have medical expenses out of the country, I am entitled to reimbursement at a rate of 80%. In the 4 years my spouse and I have been on Medicare, we have had one denial of care, after the fact. - the provider appealed, and the appeal was denied AND the provider ordered to eat the costs since they neglected to get pre-approval for one of the few procedures that require pre-approval.
Medicare Advantage, on the other hand has unpredictable expenses (allowed to be as high as $11,774 (permitted out-of-pocket max + Part B premiums) plus any additional premiums paid for a Medicare Advantage plan). You are generally limited to a specific network of doctors, generally only local - outside of an emergency. Many require a referral to see a specialist. Things considered to be expensive (MRIs, for example) require pre-approval, which is denied at a fairly high rate - not to mention the waiting period for approval at times when delaying care might mean the difference between life and death.
That said, there should be a sliding scale for premiums (or covered for all through taxes) and both dental care and pharmaceuticals should be covered without a separate policy.