It is interesting, however I don’t think the Domino theory was discredited. It was just rendered inoperable.
It was Eisenhower who first used the Domino illustration in relation to Southeast Asia. He had more in mind than just Vietnam, Laos and Cambodia.
The fear was that if those quickly fell then Thailand, Indonesia, Malaysia, even the Philippines would be the next targets. If it did nothing else making Vietnam the red line gave these other countries a chance to strengthen themselves.
As for why we had no strategy to win the war that blame belongs to JFK, McNamara, Maxwell Taylor and Lyndon Johnson. They put politics first and marginalized the military. HR McMaster’s “Dereliction of Duty” is the book to read on the subject.
I agree...it was just that an agreed balance of power stale mate had been reached. Then the aspect of mutually assured destruction and the supposed “Fall” of communism reset the chess board.