Untrue. Americans must carry a consent letter with the signature of the other parent when traveling anywhere out of the country with children. They don't need a lawyer to sign it, but they do need a witness. The fact that it is rarely enforced does not mean that a law does not exist...much like Neil encountered for his trip.
If you have full custody of your child, I do not believe this is an issue. You may want to just bring a copy of documentation showing you do. As Paulo mentioned, this is to prevent a non-custodial parent (or a parent with joint custody) from basically kidnapping a child and, of course, due to trafficking.
The refusal to submit a TM30 is illegal and the excuse that she is out of the country sounds a bit sketchy. She’s either lazy or running an illegal Airbnb rental. I arrived in Bangkok to find the following signs in the lobby of my rental awhile back. I’d recommend getting out now by contacting Airbnb about the Thai requirement to file a TM30. A host can’t just decide a law is inconvenient.
No one is pushing anything. He asked a question and you could have scrolled by. I don't have an elite visa nor do I plan to have one. However, this is an advice group. He should be able to ask his question without numerous people attacking him.