Partially right. But primarily we lost because the American people gave up. They went for the Leftist "antiwar" propaganda, they dodged, hid out, avoided military duty leaving the fighting to just a few of us, and they just voted for Democrats - which in those days was the same as voting for the enemy.
The number one reason we lost was the paucity of actual men back then.
The American people watched the nightly news...which lied to them.
We were winning.
There was no strategic plan for a victory. There was no invasion of the North. We didn’t bomb their main cities into rubble and destroy their army. That’s what worked against Berlin and Tokyo and yet neither Johnson nor Nixon were willing to do it to Hanoi. For us, WWII ran 3 1/2 years. Vietnam sputtered along for nearly 25, although not all of that was with combat troops.
At the peak of the war we never had as many 50,000 carrying rifles, the usual was 35,000. Tooth to tail was 1 to 9. By contrast the NVA was fielding over 200,000, despite heavy losses inflicted on them in battles against American forces.
Johnson’s rules of engagement bordered on the criminal by giving the NVA sanctuaries and and requiring targets to be approved back in DC. Nixon took office implying that he had a plan for ending the war, but it amounted to buying time to ‘Vietnamize’ the fight and pull out our combat troops.
Admiral US Grant Sharp was CINCPAC from ‘64 to ‘68 and wrote a book highly critical of Johnson’s policy of “gradualization” that violated everything we know about how to use military power without needlessly losing people. The book is ‘Strategy for Defeat’ if you can find it. One of the many critical examinations that I imagine you are already familiar with.