The process to legalise a document is usually embassy stamp, then get it translated and stamped by an approved translation company, then take the document to the Ministry of Foreign Affairs for them to legalise the document (or pay company to do it for you). I think the US embassy won't stamp documents anymore so might need to be done in the US before coming over.
If keeping extra money in a Thai bank isn't a concern, then a retirement visa might be a simpler option with less requirements and hassle from immigration.
preventing people being stuck in Thailand with no money and no way home? The country has nearly 40 million tourists a year (pre covid), you're thinking about how you would act, not how a system with that many people functions. Plenty of people get stuck overseas with no money.
requiring proof you're leaving a country you're visiting within the allowed time frame of your visa (or exemption) is stupid...? That's pretty standard for most of the world
the road statistic is a bit misleading though. Almost 75% of those deaths are on motorbikes. Car death rates aren't that bad, per capita it's similar to the US (hard to properly/accurately compare though)
Seen some people say they've been asked from Australia. But flown 5x from Australia in the last 2yrs on Thai Airways, Jetstar & Singapore Airlines and haven't been asked once