Yes, that is exactly how the US "lost" in Vietnam: Not having air power take them out from 300 miles away. I put "lost" in scare quotes because that "loss" is debatable, but that's a debate for another time.
The broader context was that the Indochina War was partially concurrent with, and the bulk of the combat only a little more than a decade after, Chinese intervention in the Korean War. The White House was simply terrified of the Chinese and put all sorts of restrictions on US forces that effectively guaranteed the US could never win an outright military victory.
Hanoi was declared off-limits to US bombers while Soviet and Chinese materiel flooded into the DRV, foreign pilots (including Soviets and North Koreans) were allowed to operate with impunity, airbases just over the Chinese border were used as safe havens for combat missions yet were off-limits to US pilots, over 180k Chinese troops rotated through Vietnam operating AAA batteries and such, etc. etc.
So yes, US unwillingness (arguably, inability) to apply air power where it could actually achieve strategic effects played a very large role in ensuring the US could never win an outright military victory in Vietnam. It's an open question whether the proper application of air power could have enabled such an outright military victory.
Certainly the US could and would apply air power to any serious domestic insurrection. There would be no targeting restrictions for fear of foreign escalation. There would be no influx of foreign aid and materiel. There would be no foreign pilots flying training and combat missions and no foreign troops manning foreign SAMs. There would be no foreign safe havens for rebels.
The conditions that IMO prevented an outright US military victory in Vietnam simply do not exist in a domestic context. Barring the coordinated defection of a significant portion of the US military, any armed insurrection in the US would be quickly crushed.