Maybe because the closest substitute costs 900,000 baht upfront.

I just told them I have DTV, which was fine - presumably, it comes up on their system anyway.

It's fair and reasonable, if you're a convicted fraudster with a lifetime ban on opening a bank account.

I'd like to get a Smart Visa next but it's more hassle to apply.

It's inconceivable that the authorities detained you over such a minor matter, which begs the question, who did the dragging? Regardless, the solution is obvious and easy - pay the fine and it's done. It surely wasn't even necessary to come here to figure that out, but now you're here, please explain more about this bizarre story.

I doubt many people move to a developing country, known for regular political upheaval, expecting everything to be the same in 5 years.

You should live in Thailand if you believe you will be happier here than in other countries. Visa conditions shouldn't be a major factor in your decision-making process.

electricity costs vary a lot depending on the aircon unit and how often you use it but even at the top end for a small condo, it should be more than 5k baht/month - water is basically free - but for retirement, always remember that Thailand is still a developing country with costs and prices that should converge towards developed countries over time, so if you plan to be alive for a while, be aware that everything could be much more expensive in 10 or 20 years

Unquestionably, the DTV is a far superior alternative to many other visa types, which obviously annoys people / groups who earn money from those other visa types.

Looking ahead, it seems likely / possible (nobody knows) that 2 main things could change:

1. eligibility rules could be tightened up, especially for the 'soft power' category, because it's so open to abuse.

2. the DTV and especially the 'workcation' category could become less attractive, if and when the tax authorities get strict tax on global income.

But, both of these are just possibilities, the former is just motivation for anyone considering DTV to get it ASAP, and the latter is just something that those with DTV for workcation will need to consider if and when the time comes.

However, the DTV doesn't come with enough benefits to attract enough people to have the major negative consequences on society that digital nomad visa / residency schemes have had in some other countries, so I don't see what the trigger for it being cancelled would be.

There is no need to fix your itinerary to apply for a visa to visit Thailand.