I don't think your experiences are all that unusual.
All you can do is learn from your experiences and, hopefully, find somewhere that works for you.
I tried teaching at a public high school, but gave it in after a few months. I could not really control the kids and got anxious. The other Thai teachers did try to help me out a bit by reducing my classes and sometimes sitting in. I guess they could see I was trying.
You are certainly right about presentation being key. I turned up on my first day in a suit and tie, and never stopped smiling. The headmaster thought I must be good and always seemed to favour me over the other farang teachers even though they carried more of the load and were more experienced.