the only visas that requires you to be in your home country are multiple entry tourist visa and non-OA. Pretty much anything else can be obtained from an embassy that offers services to non-residents, as most of the ones in SE Asia do. But there are definitely Thai embassies that specifically state on their websites that they only offer visas to residents of the country they are in.
that's not what getting an agent means. No one is opening an account for you. The agent just has connections at a bank that will get them to let you open an account for you for a price.
you can't be in Thailand to use a DTV anyways. So just go to Laos and get it. It's cheaper there anyways. And better than risk losing the entire cost of the visa if they ask for proof of location and you can't provide it.
One of the questions on the visa application is "proof of current location." Also they will want to see your plane ticket from the US to Thailand.
There have been multiple reports recently of embassies also asking for proof of location AGAIN a few days after the application was submitted to ensure that the person did not leave the country afterwards.
Although I haven't personally seen any reports of this type of activity from the US, it's almost not a common visa type to be applied for from the US, as most people applying for the DTV are applying for it from Southeast Asia as they are already in Thailand and looking for a way to stay longer.
Ultimately what you are asking about is visa fraud, and not a good way to get started with any government agency.
When they say it's not a valid document for opening an account, I assume they mean it's not something you can use as one of the required documents. But it's possible they mean they will not open accounts for tourist visas as well I suppose.
There's not really any news here. It's always been super easy to get a bank account if you have a work permit, and somewhat easy if you already have a retirement visa.
They clearly say anything else is up to the discretion of the bank, which is what has always been reported. You have to try dozens of banks before MAYBE you'll find one that will do it for you, but they are under no obligation to do so as there is no policy for opening an account for a tourist. It's at the complete decision of that bank branch's manager and staff.