I had no problems with using tourist visas until I hit just over a year. This was in 2018-2019. I first entered Thailand on July 26, 2018, and (with border runs, trips, etc) left on Aug 19, 2019.
It was at that year mark that they asked me if I had a flight booked to go to my home country, upon departure, which I did (but went to Australia first). I wouldn’t have been able to re-enter Thailand from that moment on without going home, thus why they asked.
If you have the “6 month” METV, you’ll be fine for up to 9 months as long as you re-enter Thailand just before the 6 month visa expires.
This is correct. I spent 2 years in Thailand (METV, border runs, etc.), with a 3 month gap inbetween to visit my home country. No issues whatsoever with immigration.