> and they don't seem to suffer from display scaling since the larger Edge 1050 runs for even longer

Why would they suffer from display scaling? At the same device thickness, larger devices have the same volume per cm² of display. And it gets better:

- if they need the same volume for electronics (likely mostly true; you may want a slightly faster CPU and more memory, but don’t need a larger GPS, second WiFi chip, etc), that means more battery volume per cm² of display.

- at small sizes, I guess/expect wall thickness of the case to scale slower than the dimensions of the case, giving larger cases relatively more internal room.

(Googling, I see the 550 is even slightly thicker than the 1050; 16,8mm vs 16,3mm)

Yes, that's my point. You might imagine an advantage for eink if you can make the display as big as you want without blowing out the power budget, but in practice it already doesn't matter.