You have this wrong.
Part C is Medicare Advantage. It paid LOWER commissions to insurance agents for many years. And so horror stories evolved about Advantage vs the higher commissioned Supplement plans like G.
Now, commissions are largely the same. Advantage plans with their $0 premiums and imposed copays are catching up.
About 40% of new enrollees are now Advantage and it is growing.
My agent (who is a personal friend) told me the commission rates...
You are incorrect.
She said that she would have to sell 6 part G plans to make what she could make with 1 part C plans.