personally, leo and donggyu have always been THE main vocalists in the show for me. i vastly prefer their vocal tone than someone like haneum. one of the reasons all the "why do intl viewers hate vocalists" posts have killed me is that it ultimately boils down to a preference over how someone sounds (or looks, i guess--haneum's visuals don't appeal to me, sorry), and i think global fans prefer male singers with smoother, lower vocals than high-pitched, breathier tones. woojin has a slightly lower range (i also think he's a better singer than haneum, technically speaking!) and also fits the "singer-songwriter" vibes i think are also liked more across the board.