I have some experience with coated nylon and Gore-tex. IMHO, I will never wear coated nylon again unless out of absolute necessity. It's water repellency (when new) is remarkable, but so is that of a rubber suit. When your inner layers get completely saturated by perspiration, your still wet.

Breathable membranes are not 100% efficient in allowing moisture to escape, but most have fairly efficient venting.

It makes no sense to dress in "wicking layers", poly-pro, fleece, etc, and then place a vapor barrier on top of it all.

Regarding ponchos, I assume they play a role in building shelters and improvised sleeping systems, but try wearing one when the wind picks up and the rain starts coming horizontally. Nothing like turning into a human sail.

Gerry