Power Armor is a miniaturized tank that walks.

Tanks have always been weak against infantry. Its why tanks never operate by themselves. They operate as the anchor of a formation, providing incredible firepower and mobile cover for the infantry, while the infantry screens the tank from ambushes and traps.. Covering eachothers weaknesses to make a big ol strength.

Power armor is certainly scary to tribals and raiders.. and may even seem like a god the walks the earth to them. And certainly in a 1v1 fight verses the average wasteland wanderer, odds are deeply in favor of the power armor.

But to an organized military like the NCR? with mobility and manuver warfare and superior numbers? Its a crackable nut.