What does 降维攻击 mean?
降维攻击 or 降维打击 is from 刘慈欣 (Liu Cixin)'s famous sci-fi novel 三体 (The Three-Body Problem).
It means that an advanced civilization uses a dimension reduction weapon 二向箔 to destroy a low-grade civilization by crushing their stellar system into a 2D plane.
If someone is not familiar with young netizen's culture or fashion, he won't know this idiom.
As you mentioned, this so called idiom can derive to any meaning and apply to any context, it doesn't need to express an exact meaning. Instead, it can express any relative meaning depending on its context. If we talk about this idiom, we should first talk about not only its context, but also its users.