''Give it a rest'' is cute phraseology. But it serves to discourage continued public interest & debate on how to most appropriately use a countries limited resources to cost effectively achieve the nations most urgent goals (Defense, Economy, Health, Education, etc) . The submarine issue may appear dead, but I'm convinced it has only been given a temporary rest. The Thai public needs to be continually reminded that any future inappropriate use of resources simply robs Peter to pay Paul.
Without getting into the weeds on the military's budget justification for their various Defense programs, I believe it would be clearly visible to experienced military budgeteers that the Korean trainer jets are most likely far more easily defendable on multiple issues, than are the Chinese submarines. Total Life Cycle Cost being the most immediately obvious (look at the aircraft carrier "Chakri Narubet" sitting idle tied down in Sattahip).
At the risk of over simplifying, primary among such issues would be (for each of the various alternative ways to accomplish a stated mission) a Total Life Cycle Cost vs Performance Effectiveness Analysis. The Korean Trainers would most likely pass muster, whereas the Chinese submarines would very possibly fail scrutiny; especially in competition with other Thai national requirements (Health, Education, etc, Peter pays Paul).
Then there is the "Faustian Bargain" issue. I'm guessing that the Chinese Communist Party (CCP) has siezed the opportunity to offer a submarine program "Loss Leader" (perhaps with "back handers"). Like their Belt & Road initiatives, the purpose being to grab the Thai military by the "short hairs".
The Thai submarine program would then in future be dependent upon the CCP for Chinese submarine unique assistance & advice on all of the following: Doctrine, Organization, Training, Logistics (Supply, Maintenance, Transportation), and Materiel Upgrades.
The CCP knows what it is doing. A grandiosity seeking, seemingly naive Thai military leadership very possibly does not appreciate the ramifications. The Thai public should be continually reminded.