extension is a lot quicker. How much so depends how close you are to a border/airport. Certainly if extensions are 1,900 but even if they are 10k I could see people choosing to extend in country if they don't want to leave for some other reason.
it's also not clear that the extension will be 10k. I know there was talk of that when it was announced but every other extension is 1,900, regardless of the type or duration. It could go either way but I suspect the extension will be 1,900 same as everything else.
yes and retirement is 800k but this is a different visa. It looks like they just want to see 500k once at visa issuance too, it doesn't seem like there is any ongoing requirement to keep showing it.