There is this obscure setting you can enable to be able to click anywhere on a window while holding Command + Control to move it.

defaults write −g NSWindowShouldDragOnGesture −bool true

This only supports moving around windows, not resizing.

After a bit of testing, the target area seems to have certain dimensions that are based on pixels (19x19 according to OP). With a lower resolution, the corners become much easier to grab. I have had no issues resizing windows, and I'm on 26.0 (25A353).