For about 10 years, off and on, they have been saying that all the while I was able to do it... Not only that, you can get a visa while in Thailand.... "days coming to an end" bah hum bug.
"I just like to really understand what's going on" Good luck with that, this is Thailand and I am pretty sure nobody knows what is going on.
To answer your question. What I was told was, I MUST use the 800K method to get the visa (year 1), To renew the visa I could do the 65K method.
However, I use the Pattaya immigration office, which may implement policies differently than your father's immigration office.
I use an agent (because I didn't have the 800K, agents can provided that for you).
Pattaya's immigration office is known to be openly crooked so it could be the case that I had to use the 800K only because the agent would make more money. Or the immigration office would make more money (bribes).
So I wouldn't say your father's situation is exactly the same.
That will be the case with most advice you get from Facebook.
Different immigration offices - different rules
Different nationality - different rules
Different "friends" - different rules.
The Thai immigration site is probably a good place to get "guidance" but in the end, its up to the immigration office which/how rules get applied.
Sounds like they know what they are talking about, which is kinda rare.
I couldn't speak to your father's case and it sounds like there is some confusion.
The rule is, pretty much. You must have 800,000 in the bank year round OR show income of 65K+/month. The funds MUST come from overseas (that gets some people but I think not a concern in your case). You do not have to do both.
I recently got my first retirement visa (800 for one year required). Next year when I renew, I should be able to get the visa by showing that I have income of 65K+/month, from overseas.
You should be aware, every immigration office is a little different. If you're working with someone to get the visa, they likely "have a friend". Although, in your case, it sounds like they do not, and you're doing every thing by the book and the book is confusing (by design no doubt).