Of course the Vietnamese could never have beaten the US in an actual war nor is that what happened.
To recap- Vietnam was a false flag. It was a war of aggression, as was the incursion into Cambodia.
https://en.wikipedia.org/wiki/Gulf_of_Tonkin_incident
"Later investigation revealed that the 4 August attack did not happen; no North Vietnamese vessels had been present. Shortly after the events, the National Security Agency, an agency of the US Defense Department, deliberately skewed intelligence to create the impression that an attack had been carried out.[5][6][7]"
So, leaving aside the history of France in Vietnam, Vietnam was invaded by the US. It's that simple.
Vietnam was not and never could have been an existential threat to the US.
If it had been, hypothetically, it would have had zero chance of winning an actual war with the US.
The only thing that happened (and the same with Aphganistan and Russia) is that Vietnam "won" back their countries through attrition.
As an aside, do you think the US had an actual intention to occupy Vietnam on a permanent basis? I don't.
So, we get to Ukraine.
Again, Russia won't occupy Ukraine. It might change the map. But that's different.
So, why is Ukraine attacking Russia as if Ukraine can "win" the war and set the terms for peace?
It's not going to happen.