There’s a difference between drawing visual and thematic inspiration from Vietnam, and doing a full-on allegory about the Vietnam war. And if Star Wars really was meant to be a Vietnam allegory, then it’s a really bad one for several reasons.
George has always been one to speak bluntly. He’s not gonna beat around the bush and say something like “I drew on the visuals and themes of Vietnam to enhance my story.” He’ll just say “It’s about Vietnam. Palpatine is Nixon.” Because he speaks bluntly. That doesn’t make it a full allegory, necessarily.
While I appreciate the note about Cosmonaut orange there are few real references to things in the Cold War (you’d have to ignore that Yuri Gagarin fought the Nazis not the USA). The Imperial troops aren’t wearing tiger-stripe green and being entrenched in guerilla warfare. The WW2 stuff just overrides almost everything else. They’re not in an arms race, they trying to stop one big new weapon like the 1940s. They’re not a down and dirty faction using any basic tools they can, they’re equipped with fighters that in many cases are better than the big bad have, like in the 1940s.
Admittedly the like of Rogue One and Andor muddy the waters but the point stands. “Palpatine is Nixon” falls apart because there’s no opposing leaders to fit that analogue. Are the leaders from Yavin the Chinese? Are the Mon Calamari the USSR? Even if he did say “I drew on the visuals and themes of Vietnam to enhance my story,” then it falls down. Which is very funny when you think that James Cameron is the one that has made multiple films built in incredibly blunt 'Nam references.