But to say that color alone makes it better than greyscale… No, I can not agree with that. A matter of taste? Perhaps. But there is some absurdly beautiful art in Manga too.
Starkness, working within constraints, has its own beauty.
And, as an aside, full color manga is becoming a thing too. More and more full color webtoon style comics are coming from Japan; from mangaka.
Since full-color as a set technically includes the B&W set (and in the case on point of Solo Leveling, there are some scenes that are notably impressive while being mostly B&W! or grayscale with a shadow hint in other color) then it's a truism that full-color reaches to heights that B&W can never reach.
Halftones, delicate hatching and thin lines all turn to mush when anti-aliased, so they just won't show up in a medium optimised for grabbing the attention of the infinite-scrolling phone-reader with thumbnail-sized images.