100% agree with your post. furthermore, you can add Northeast Issan and Buri Ram, Si Sa Ket, and Surin to that list as well.
While these regions I mentioned are considered Thai citizens, the majority are Lao descent and speak Lao/Issan language at home and to each other. Same thing goes for the Khmer descent in the southeast part of Issan near the Cambodia border. Thailand has attempted in the last 7 decades to assimilate the people in those regions to think and believe they are Thai, but in reality, it hasn't worked so well.