Some people turn that around and say that at least Diem had some authority and when he was killed we really lost a chance to win. Hard to know what to do under those circumstances.
I didn't find the series sympathetic to North Vietnam or the Viet Cong. The focus was more that with enemies determined to lose millions of lives there was no way we could have won (without utterly destroying the country and our own reputation).
But I still say, the US didn’t lose the war, South Vietnam did.
Vietnamization was never going to work.
That’s the way I saw it also.