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.

Didn't NCR defeat BoS only through heavy use of logistics, long siegies, and mixed unit types? NCR has tanks, trucks, infantry, vertibirds and such. It's quite literally the only modern-like nation in Fallout universe as far as I remember. All of their vehicles are a bit limited, but still. They were able to basically position BoS how they needed to then siege them out.

At least as far as I remember the tidbits of lore.

Enclave is a bit different, because Enclave isn't any worse when it comes to logistics, so there is no waiting them out. And Enclave is not afraid to use old tech, to which they do have access.

Truth is I don't see how Enclave could lose. In metro tunnels, the fact they have fewer, but elite units plays to their advantage - there's a limit how many people can stand arm to arm there. In open space they are faster and tire slower than enemy, without the weakness of BoS logistics, while their armor does give them defense against anything less than a rifle. And we know Enclave also has artillery and most possibly other mechanised support so yeah...

Simply tech gap seems to big.