Personally, I think a lot of these "screen problems" are due to a difference in our own vision accuracy. Some may see these minute variations as large and others simply may not be able to see them at all. Those with better vision may see problems where those with poor vision may not see them.
In addition, we may be comparing the eInk screens to LCD screens. eInk will never be as clear as LCD but LCD has more glare in bright light than eInk.