I'm a Filipino and I worked in the BPO industry for more than 6 years. I and my colleagues were trained by Filipinos both in product and English. I can say that they are the best teachers because they explain everything in detail. The clients who happened to be native English speakers from The USA never had an issue with it while they were observing the class.
It's funny to imagine people who barely speak or understand English would say that they don't understand us when we speak, while it's they who struggle with comprehension in the English language.
Thailand sets its own rules and it's understandable why they prefer Caucasians to teach them but ultimately, the purpose is to learn. If they don't want to be taught by a Filipino because we aren't the epitome of a native English speakers, that's cool. It won't diminish our language/teaching skills.
I'd suggest to my fellow Filipinos to not constantly seek validation from foreign people of our self-worth and ability because they will never do the same for us. It makes us look pitiful in their eyes. We should show them that we don't care about their negative opinions because we know ourselves and our capabilities.
It's better to do our own thing and be good at it than seeking attention from people who look down on us. Success is not determined by praises and fame but rather results.