[Quoth]

There is more to display quality than contrast. OLED certainly wins on contrast in a dim or dark area. LCD can be better in direct sunlight if a matt screen/filter and sufficient backlight power as OLED isn't real LEDs, but electroluminescent dots with phosphor and limited in power. QLED is actually LCD with pure blue LED backlight and quantum dots for red and green, so can be about x6 brighter, or 1/6th power.

With Carta you already have sufficient contrast and brightness for any ambient light good enough to read a paperback, and often Pearl is good enough if no layers.

Each layer reduces contrast: colour (printed ink for colour on eink or LCD or phosphor and CFA with OLED), a light pipe on top (eink), capacitive or resistive touch layers because each layer will reflect some light.

One aspect of increased contrast on Carta 1200 or maybe 1300 is to reduce layers by at least one by integrating capacitive touch and light-pipe rather than selling a bare eink panel to the OEM.

A matt top layer on LCD, OLED, QLED, VFD, LED and historically on plasma and CRT can increase contrast by being tinted as emitted light is attenuated once and reflected light off the interior panel is attentuated twice. That can't be done on eink unless you have it only front lit as it would attenuate ambient light.

So ultimately only mono eink has an advantage if ambient light is enough to read without front light. The front light lightpipe also reduces the sharpness and ambient brightness and ambient contrast a bit, hence a Pearl panel with IR touch and no front light can be nearly as good as original Carta with a front light and capacitive touch.

People say the Kindle Voyage has the best 300 dpi 6″ screen. The top surface is micro or nano-etched glass, so expensive compared to plastic matt surface and likely sharper. It also must have used a more expensive light pipe for the front lighting. The Oasis 1 is same panel (6″) so essentially the mythical Voyage 2 of goodereader. The paperwhite 3 is essentially a cost reduced Voyage (300 dpi 6″) and better than the paperwhite 4.
Yet by all accounts the earlier Voyage is better.
The Oasis 2 & 3 are 7″ and the Oasis 2 I had was no better than the Libra or Libra 2 (I had all 3 at the same time).

So it's complicated. But five things are clear:
1) If it's too dim to read using ambient light, you need the front light on and it's then just as emissive as LCD, as it's LEDs and a diffuser in front and LCD is LEDs and a diffuser behind (light pipe). The eink light pipe is more expensive as it mustn't blur the text. The LCD light pipe can be rubbishly cheap (the bad ones let you see bars/stripes of shadow).
2) The Kaleido 3 is printed coloured dots of red green and blue that don't cover the pixels, so it's pastel. They reflect, so contrast and brightness is reduced. Light has to go through them twice, unlike LCD stripes or dot colour print (LCDs are mono). So Kaleido eink isn not only poor colour but degrades the sharpness and contrast and brightness of the mono eink. You need the front light indoors, so it's emissive.
3) There is no advantage at to eink listening to audio books and it might be inferior (choice of supplier, no 3.5mm jack on Kobo or Kindle, charge run time).
4) The 4096 "colours" of Kaleido is not as big as it sounds, because that is all variations of saturation, brightness, contrast and hue. There are shades of pastel and murk, no nuances because the underlying mono eink is white, black and just about 14 greys. The LCD, OLED, QLED etc panels are mostly about 16 million and some do much more. You can actually simulate kaleido quality that's using a front light on LCD, OLED or QLED!
5) Kaleido is only 150 dpi in its poor colour. In mono you can't have the true 300 dpi of the mono panel. Driving at 300 dpi rather than 150 dpi in mono results in coloured artefacts. The coloured dots are printed translucent ink and there is screen door effect because they deliberately don't cover the pixels, so as to allow both a pseudo 300 dpi mono and to brighten the panel at expense of making colours at most pastel shades. Tertiary colours are thus poor.

Conclusion, only mono eink in ambient light with zero frontlight is totally like reading on paper and nothing else can quite match that unless the room lighting is completely diffused, or you are outside under a very overcast sky.