Gotta do what they can to hide the 356p resolution graphics Seriously though it probably has more to do with battery life.. maybe?
I think the contrast on the Switch's screen is just poor; it has dark darks and very bright brights, but the values in between them are low. grey's are either very dark or very bright.
There is a pretty easy to access and wide variable brightness slider if you hold the home button down, and the brightness on full bright is plenty bright; even at its brightest there are dark areas.
I wonder, actually, if these games don't have a high ambient brightness and the fake HDR exposure is just crunching values so low (XBC2 and Skrym both have fake HDR / Exposure based illumination)
And yes, that shitty low resolution is not doing any favors for the brightness. Screen brightness for exposure is calculated by how many pixels are of a brightness vs the rest; so if there are only 356 pixels and 1/4th of them are darker than the rest, those will be extra dark as the engine tries to force crunchy exposure values. Where the game would display grey values the scaling resolution will clamp those down into nearby values, causing exposure to get wacky. Personally a more static lighting setup would have been preferred but I doubt they planned for that low of resolution, and hopefully as performance patches come down the pipe exposure will benefit from the higher resolutions.