At private schools money talks. Bigger classes is more money. To reduce the class sizes the fees will go up to international school standards I'm afraid.
Schools also don't need to hire teachers with a teaching degree. I was amazed to see so many colleagues with no teaching background whatsoever. Some of them are really good by the way. On the other hand I see teachers with a bachelor in education or higher with no teaching skills.
In government schools you have, on paper, qualified teachers but in many cases they don't have the motivation to make a difference. Many didn't choose education because they love it.
I agree that many lessons that I have seen are grammar-based (Thai and Filipino). Not saying it is wrong, but it is not my way. On the other hand there are a lot of teachers that come through agencies and are not staying longer than a year (sometimes two). That way you can't build consistency. Yes, if management is amazing it is probably possible. But in general, new teachers have to find things that work and don't work by themselves again.
To keep teachers longer will be hard. The demand of good teachers is high and many native English teachers will go to international schools. Even good non-native speakers go to international schools. What is left are many teachers, but nowhere near enough to fill schools with middle-class children.
Also the communication to parents is something I obviously agree on. I work at a school where 95 % of the parents speak at least basic English and are all on LINE. Also they are open to talk to you after school. In my previous school, half of the parents could speak English but many of the kids lived with grandparents. They didn't speak English and were not that engaged. It was more difficult to reach these (grand) parents.
In my opinion the biggest step forwards that Thai education could make is improving the teachers. I know that the government spends a lot of money to improve teachers. At the moment this money goes to trips around the country with no benefit to the schools whatsoever. Also colleges get a lot of money for buying equipment, but most of that money goes in people's pockets I'm afraid.
I hope the government could change this somehow. Also monitoring schools is based on documentation rather than (classroom) observations. I think there is enough room for improvement here. Whilst not seeing the whole picture, I think this is the first thing to change.
Knowing that my English isn't perfect (non-native English speaker here) I hope that my reply will be commented on content rather than its grammar and spelling.