Looks like you did not understand that comment. Concrete will not let a draft through no matter where the wind hits. For fiberglass and others, one bad fitting means a current can form through the material. This is why you need tyvek to begin with.
You are misunderstanding the American building system. We don't use fiberglass insulation by itself. You're picking a small part of a greater system and complaining it doesn't work in isolation. There are multiple layers to our construction and it's effective.
As for the wall material stopping drafts in a window frame, that makes no sense at all.
Exactly, the critique is that you need multiple layers, and if one fails, the R values you thought you had go out of the window. Whereas a concrete, wattle and daub etc wall will tolerate less-than-perfect fitting and maintenance. Of course if you assume construction is flawless, there will be no issues, and that’s the usual case.
A poor fit, minor damage, or any defect allows convection within the fiberglass. R-value assumes zero air movement, which is why it is far less useful comparing fiberglass to foam or aerated cement. In real world settings, aerated cement will outperform fiberglass.
The same thing can happen when concrete cracks, which is quite common. All of this a question of basic building maintenance rather than the building materials chosen.
Cracking is why single family homes generally avoid concrete walls in the permafrost.
