I've heard rumors of this for a decade. Never met someone it happened to. I've never seen it happen when i was sitting at immigration and it's certainly never happened to me.
That's interesting. They told me only 12 months. Maybe I misunderstood. Also 12 months to 3 years is not correct since the first course is only 4 months long
2 hours a week won't get you shit unless you're some kind of language savant.
Spanish is literally the easiest language on Earth for an English speaker to learn so I wouldn't use that as a gauge. It shares words, shares some grammar, shares an alphabet... none of which is true of Thai.
Thai is hard and if you want to speak it you'll need to make it a very big part of your life. Daily practice, for sure.
I would say minimum 1 hour of serious study per day, but even that will be pretty slow. I'd want 2-4 hours of serious study every day if you want to pick up the language before your ED visa expires
as far as "a waste" it depends on what you are in the school for. If you want the visa to enjoy Thailand for a year then it's not at all a waste not to practice. It's a good use of time. But if you want to speak Thai and all you do it attend one 2-hour class a week? LOL yeah it's going to take you 200 years