In the end I had to do it the hard way (I am used to it in SpriteKit now) and used a series of logic gates before executing on a switch statement to arrange every node.
I found netshark1000's contributions on a StackOverflow posting really helpful as there was no built in Apple solution to getting info on the model of device in use: ios - How to determine the current iPhone/device model? - Stack Overflow
I don't know why Apple doesn't have something like this built into Swift, it seems like they really should have:
switch UIDevice().type {
iPhone5, iPhone5S, iPhone5C, iPhoneSE : // 320 x 568pt | 640 × 1136px
iPhone6, iPhone6S, iPhone7, iPhone8 : // 375 x 667pt | 750 × 1334px
iPhone6Plus, iPhone6SPlus, iPhone7Plus, iPhone8Plus : // 414 x 736pt | 1242 × 2208px
iPhoneX, iPhoneXS, iPhone11Pro : // 375 x 812pt | 1125 × 2436px
iPhoneXR, iPhoneXSMax, iPhone11, iPhone11ProMax : // 414 x 896pt | 1242 × 2688px
iPadMini4, iPadMini5, iPad5, iPad6, iPadAir2, iPadPro9_7 : // 768 x 1024pt | 1536 × 2048px
iPadAir3, iPadPro10_5 : // 834 x 1112pt | 1668 × 2224px
iPadPro11 : // 834 x 1194pt | 1668 × 2388px
iPadPro12_9, iPadPro2_12_9, iPadPro3_12_9 : // 1024 x 1366pt | 2048 × 2732px
}
As you can see, there are a lot of screen sizes, but mercifully some do overlap. UIDevice.current.orientation.isLandscape / isPortrait doubled my workload, and in the end I locked the orientation as the screen will just not organise sprites if freely rotated (I still have the original problem).
I also needed more granular control when in landscape as my sprites were too cramped compared to portrait, which made a lot more work necessary as they would need to be substituted as can't scale my sprites without a noticeable visual loss in quality.
However, this does give me granular control and it did "work", but the orientation must be locked, which is a shame, but nobody seems to know how to allow for sprites to reorganise themselves after rotation. The closest I saw was on the pause menu in CrossyRoad, but they used a trick that kept everything compact enough in either rotation.