Yes I left my money in Australia earning 11% tax free and used the "insurance declined" proviso of the OA to get out of buying a useless policy! It's a no-brainer!
I switched from OA visa which I'd had for two years and had transferred 65k per month for almost two years. I did an out/in, got the non-o visa and went straight onto 65k transfers with that. Never needed the 800k lump sum
I've had the non-O retirement visa for several years. I've no idea what changes you're talking about. It's been the same process for me every year (at Bangkok Immigration)
The first year (unless switching off an OA visa which I did a couple of years ago) requires the 800k in the bank for the first year of the visa/extension. If you also start the 65k transfers in that same year, you will have 12x transfers by the time you extend for the second year, so you can then withdraw the 800k