I don't use e-ink, but I have astigmatism and dark themes are difficult for me to read, especially really dark high contrast themes (white text on black background), so I pretty much use light themes almost exclusively, even at night (I just turn my brightness down).

So I agree, default to whatever you want but definitely keep an option for a light theme available for those few of us that prefer it.

FWIW I don't prefer white themes either, I like something like solarized light or gruvbox light