So I’m researching to understand what the draw back of the HMO plan, besides less choice.
There could be no other HMO drawbacks. Just the possibilities that you won't be able to get a new provider you prefer (e.g., a specialist for a new condition) or that provider services could involve more delays. I think of PPOs as a way to pay for more peace of mind.
Providers can change which insurance plans they accept, from time to time, but there's not much you can do about that.