Launch Screen vs. Launch Images

Lifted since I cannot post there
Use a Launch Screen only
Launch Screens are set up using autolayout so they certainly should scale nicely esp if you use an image set with 1x, 2x, 3x resolutions in it
They work in all new versions of iOS (8 and up)
The launch screen automatically selects the right image resolution based on dpi etc
So fill in the 1x, 2x, and 3x slots
Make sure if your 1x image is 128 x 128 @72 DPI your 2x is 256 x 256 @ 72 DPI and the 3 x is 384 x 384 @ 72 DPI
Lock the image center or to edges which ever way suits your needs
And make sure the Content mode is set to fill scale etc as you want as that will affect how they work