I read manga on my kobo elipsa 2e (10" 227 PPI, 1404 x 1872 resolution) often and find the experience quite good. I specifically got that e-reader since it has a big e-ink screen. Manga is mostly black and white anyway and the color pages get shown in grayscale, that works relatively well. I suppose traditional comics also work well since they have black text on white background the color to grayscale may cover some detail but should definitely be readable. most color comics and manga are printed in 300 PPI.
I'm not satisfied with a grey scale screen given it doesn't work for 99% of comic books and a significant amount of manga (ghost in the shell, for example, has a large number of colour sections)
A lot of physical manga volumes reduce what would have been originally colour pages in the serialization to B&W anyways. Heck, it's verrry common for that to include the eBook edition even though it doesn't really cost them anything.
Ever experienced the bug where usb loaded kepub manga disabled bookmarks and annotations?
https://github.com/ciromattia/kcc/issues/704