Let's not forget that the Easter Offensive in 1972, while an utter failure and disaster for the North Vietnamese in their attempt to take urban centers and destroy South Vietnam, did manage to successfully overrun and keep the Central Highlands. While not a major population center, it provided an excellent safe zone within the South for resupply and rebuilding. Note as well that without American advisors, FACs, and pilots, ARVN would have utterly collapsed in 1972.

Also focusing exclusively on successes in the counterinsurgency battle ignores a critical aspect of Maoist revolutionary warfare, which prescribes transitioning to conventional forces as soon as possible. The Communists in China didn't win due to guerrilla uprisings in Nanking --- they crushed the Nationalists in the major force-on-force battles, where guerrillas acted primarily as guides, supply, and political mobilization rather than playing a significant military role. The same thing happened in Vietnam, except when the major conventional campaign occurred South Vietnam fell far faster than the KMT in China.