I agree with bpcyclist. Something feels funny here. It sounds like your pdoc is projecting onto your potential future quite a bit.
Rationally speaking, the notion that you will dislike a town or city or region simply because his close friends did is a stretch. There are happy people and miserable people everywhere you go. It is truly about state of mind and the company you keep. I would think a pdoc would understand that better than most people.
Healthcare concerns are perhaps a bit more his lane, but the argument still has some holes in it. Healthcare is a product of the systems as well as the practitioners. The system in America is quite broken in many places and some practitioners are criminal to say the least. Conversely, there are components of the system that are beneficial and some practitioners should qualify for sainthood. A French pdoc sending a patient to America could air out quite an extensive laundry list regarding the mental healthcare system here.
The issues created due to the rules of a system and the users of is not unique to healthcare. This is the state of any large system in a major county. They have holes and strong points. Practitioners and users can make them shine or exploit them. You can choose to focus your attention where you wish.
Personally, I wish he had taken more of an educational approach. It is one thing to offer someone information to ensure they are educated and it is another to fearmonger. I feel his approach with you boarders on the latter.
Mostly I wish his focus was on you and your state of mind while making these decisions. He should potentially be working to ensure you have spent time considering the options while in a balanced state. He should be working to ensure you have a medical care plan during and after your transition. He should be concerned with whether or not you'll have the emotional support you need. It appears to me those components aren't a worry in your case. You've mentioned this move here several yimes while of sound mind and a state of balance. You and your husband are very intelligent people capable of weighing the pros and cons of such a complex endeavor.
I know you respect your pdoc a great deal and he has offered you tremendous value in your journey over the years. I'm not trying to bash him, but I do feel several things were amiss with his counsel. It feels emotional and rationally has some areas of concern. I imagine this is related to how much he genuinely cares for you. I wouldn't hold it against him, but I also wouldn't let his negativity hold you back or create unnecessary fear or stress. Worst case scenario you go and you hate it. The thing about moving is it isn't a one way ticket...
I wish you had been given more positive support. I'll offer that. I hope that no matter where you land it offers the joy and stimulation you crave while also fostering the balance and stability you need. I hope there are kind souls there and potential lifelong friends. I hope you feel cared for healthwise and in other ways by the community. I hope you feel you can foster a sense of purpose there. I hope it adds value to your marriage and you and hubby go on to enjoy many more wonderful years together.