Looking at epub and pdf after adjusting text and icon DPI on opensuse makes this stuff very washed up, specifically if you hiked up DPI while still using bad screen :P (that comes with laptop).
HiDPI support landed today with https://cgit.kde.org/okular.git/commit/?id=ecc1141e0293e1a30e0f8787d86dcc6309ffb0c0