Yeah but by then the U.S. presence was all but nil so the NVA had enough of an advantage with tank numbers.
If there were still significant U.S. forces in there, they'd have had tanks ready and able to defend the city and its doubtful the NVA tanks would have had much chance against them. But even then, its the U.S. Helicopters which would have done the real damage to any NVA tanks which had shown their head.
Low tech armies/forces/countries usually have only troop advantages. They might not be as well trained or equipped but they have lots of them and they're more willing to put up with casualties than Western forces, so they keep to areas where tanks and other higher tech equipment can't be easily brought into the fight. In the case of Afghanistan and Iraq, all they have are mountains. Outside of that, the best they can do is keep to small groups in the cities and make small attacks of opportunity while trying to slip around under the noses of the enemy. This is why Mechs could be important if they get it right. Suddenly, western nations could bring technology into the mountains and forests, capable of withstanding light arms fire and returning fire.