I work offshore half the year and live in Thailand when not working. Having a proper long-stay visa like the DTV is a huge benefit. For example, landlords will be more receptive to renting to you. It'll be easier to get a bank account, driver license and an auto. For US persons a solid visa is a de facto requirement to claim tax breaks like the FEIE.
For the DTV, I would advise you NOT to apply under work-cation/freelancer status. Even if you could get an employer letter approving remote work, The risk is that the person evaluating your visa application may correctly determine that you are not actually going to be working in Thailand and deny you on that basis. Instead, apply under whichever of the soft power categories is most interesting to you. The bar for qualifying seems to be very low for all of them.