many people choose not to use them, i prefer to use cash as give myself an allowance every Friday and watch it drop. When finished I stay home! Scan is great but no control!!
They have new promotions constantly rolling so probably you struck lucky. Some banks as you mention have put limits on transfers and some stop use of apps if over 70. Apparently many people in that age group are vulnerable to scams, especially locals so sadly a new regulation
I am from UK BUT always send sterling and take the better exchange offered in Thailand. When you select Thai baht you are given a rate as you mentioned, so then as a comparison Google the bank you are using in Thailand and check Telex transfer rate. That's what you get when send $ less admin charge about 350 baht
If you are sure you existing policy covers you for the duration of your stay, it is not necessary to have health cover in Thailand, many choose to self insure instead. The cover against a visa only applies to an OA visa where no funds are required here as the visa is issued in your home country