You have to take into account the technology that existed at that time.
Using Tactical Bombing in a very strongly defended target area and getting direct hits on structure that either destroys the bridge is a tough chore until precision bombing using guidable bombs came along....which it did in 1972
The US Navy dropped the Thanh Hoa bridge using then the latest tech guided bomb available.
With today's bombing capabilities.....dropping a bridge is no problem.
Dodging SAM's and AAA remains an issue for sue but with the standoff distances possible now that risk has been lessened.
But....getting back to flying the Herc at night without Terrain Following Radar or NVG's down the river was a very courageous act bordering on the insane.
They succeeded the first night then should have given it up for good....going two nights in a row was needless sacrificing a crew of very brave Men.
Of course we can say that of the entire bombing campaign called Rolling Thunder with all of its ROE Rules that prevented the Air Force and Navy from doing their jobs effectively and only resulted in Pilots and Crew being killed or captured for long periods of imprisonment, torture, and far too many deaths.
That was until Nixon turned the Air Force loose and sent the B-52's to Hanoi and mined the harbors.
That following on the heels of the tactical disaster of the Tea '68 attacks....which failed. miserably militarily but was a strategic victory by winning. over the anti-war sentiment in the United States is what finally brought the War to an end after Congress ended support for Vietnam and Cambodia Operations.
We can lay the defeat at the feet of LBJ, McNamara, Westmoreland, the Joint Chiefs, and some others who fabricated a War, who never intended to "win" it in the nature of WWII, and made decisions based upon domestic considerations rather than on genuine military considerations,