@Andy ***********
Firstly it's only "doesn't get much simpler" when you give zero context and only base the information you're sharing on what you have been able to do with the visa YOu arrived on... secondly a visa and extension of permission of stay are two entirely different things, you cannot extend a visa.
And again if you arrive in country on a 90 day NON-O (NOT A NON-OA) your only options are 800k, an income affidavit from YOUR embassy or using an agent, the only except to this is if you already have a bank account that you have continued to transfer 65k+ into for over a year (however the vast majority 97%+ are unable or haven't done this, so its a moot point). If you convert to a NON-O in country again your options are the same.
Flatout claiming "it doesn't get much simpler" while negating and ignoring all information and variables is a fallacy at best, and completely delusional at worst...