That is just simplistic and not true
Your first paragraph is true.
Your second paragraph is just wrong. If it works for you, that makes you one of the "I've got mine, screw you!" group. People do NOT have a choice as to who their carriers are. IE at my workplace, they contract with one HMO. That's it. No choice.
I've got mine and it has worked well for me almost all the time, except for a few minor things. But I'm not one of the "I've got mine, Screw you" group. I want coverage for everybody and no friggin' HMO telling some poor soul who is dying of cancer that the treatment that might save him or her is not covered.
God help you if you or your family ends up one of those situations, because the HMO won't!