Yes. War is an extension of politics by additional means, casualty ratios mean very little in terms of who wins a war except to the extent to which it allows a force to ultimately achieves the military objectives it has in a conflict. The united states had the fire power and troop quality to successfully win tactical victories but it was never able to actually achieve its major objectives of producing an outcome in which they could successfully produce a situation where South Vietnam could survive and resist the North.

On the subject of dominating the north this isn't the case. The united states never actually invaded North Vietnam, it bombed its cities extensively but they were already in a situation where their resources were stretched attempting to protect South Vietnam where they at least had some local support. Extending their forces to invade North Vietnam would have stretched themselves thinner and as the French found in their own conflict in Vietnam the border of Vietnam with China would have been an extremely difficult one to police, the mountainous jungle environment would have allowed Vietnamese forces to retain a presence there more or less indefinitely harassing the US forces in a region where they'd now have even less forces and where their enemy would still be able to get supplies from further north still.

So what was the situation as the US involvement was coming to a close? Well the US had recently manage to engage the Vietnamese in some fairly large scale exchanges and come out well on a tactical scale. However the effect of US casualties on the willingness of the American people and politicians to continue the conflict was not equal to that of the effect of Vietnamese casualties on their willingness to continue the conflict. The Vietnamese were more invested in the outcome of the conflict and between US casualties and the civilian casualties produced by the war undermining the US public's moral belief in the conflict the US's presence in Vietnam was increasingly unsustainable. It was precisely that the Vietnamese were willing to win the war no matter the cost and the US was not, it was not a war of necessity for the united states, that allowed them to win. And this is in every sense still a military failure, the will to continue a conflict is a strategic resource that must be managed and spent with care. A military that wins tactical victories but has their government lose the will to continue the conflict when they are unable to achieve their strategic objectives has no more won a war than if they had run out of food or steel or bullets with which to fight it. So the US seeks a way to withdraw.

They go to Vietnam and looking to save face officially draw up a peace agreement, the US will leave sooner rather than draw out the inevitable and the Vietnamese will officially sign a peace accord. But you have to considered at this point that such a peace accord was meaningless except so far as it let Nixon save face in that it allowed him to obfuscate the US's failure to achieve its objectives given that once the US was gone the US and North Vietnam both entirely knew that the US had withdrawn from Vietnam the Paris peace accords would be a meaningless piece of paper. That the US had failed to put South Vietnam in a position where it could stand on its own two legs. Its military wasn't capable enough, and its government neither popular nor competent enough to wage war against North Vietnam without outside help. And so with the US unable to stay South Vietnam collapsed under the pressure.