If it wasn’t a formal requirement the airlines wouldn’t care. But they are required to check if the passengers fulfil formal requirements and can get fined with 10 000 USD and be responsible for your return if the immigration ask and potentially deny a passenger.
You can only do one extension unless you’re married Thai or have a Thai child. Best option is to get a six months multiple entries tourist visa before you come in order to avoid going back to back on visa exemption.
But you still have a void stay in Thailand even if your personal benefits it’s more important than to fulfil the requirements for a legal stay in a country you choose to live.
I understand. Still a tourist entry though but it’s slightly easier to get approved with a formal document. As said personally I would have considered to use a landborder transport company. They’re fairly priced (3-4000 baht), know the "name of the game" and wouldn’t bring you unless they’re confident in getting you another visa exemption.
To avoid going back to back on visa exemption I guess. As said can slightly increase odds for a "clean" entry. Personally I just would have used a landborder transport company to bounce me for another 60 days visa exemption if that was the point.
Then I’m not sure if I got your question, but a Tourist visa has been 60 days for a long time and is still useful for people who are not entitled to visa exemption or if the exemption is turned back to 30 days again. A tourist visa can also slightly increase your chances for a new short stay entry in fact only because it’s a formal document. Both gives you a 60 days stamp and permission to stay for 60 days upon arrival.