GLPTs aren't really inherently responsive (though you're right that they're framed that way). What they are, in contrast to FFLPTs, is "not not responsive." That is, the way elements are rendered in FFLPs makes it mostly impossible to have the same HTML for multi-mobile and multi-desktop (which is why they need to have a "mobile version").
GLPTs allow you to use responsive design techniques without overriding anything you want to do. But you still need to follow responsive guidelines. It's still perfectly easy to build a non-responsive GLPT (or have a seemingly responsive GLPT behind a non-reponsive LP because of tweaks made at the LP level).