I find that the complexity is much reduced if I start the design for an iPad Mini portrait base. For smaller screens (physically) you can fit the same information, but you may need to re-arrange it making the page taller. For bigger you can tweak it or not.
It really comes down to use cases. If it’s an administrative interfaced used for hours on end, you probably want to improve the layout at 1200+
If it is brief interaction/casual it’s probably fine without further layouts.