its not wrong TDAC is Thailand Digital Arrival Card it is not an ETA system (Electonic Travel Authorisation). The TDAC is the old TM.6 that you filled out on the plane just digitalised 🤦♂️
TDAC doesn't accept or deny you. That system hasn't been put in place and has been indefinitely sidelined until futher notice. The TDAC is just the TM.6 in digital a format.
You need to ask the embassies themselves if you want accurate and the most up to date information. HCMC I've no clue about. However, according to a friend applying soon, London right now want to see 11k+ banked for a minimum of 3 months.
There is no law or rule limiting visa exempt or tourist visa entries. You can do it until you can't. For some that's 6 or 7 entries in a short span, for others in 2 or 3. You are correct though, if youre going to come regularly, get the proper visa for it