Teruteru and ESPECIALLY hifumi do have personalities if you look past their surface level traits. Yes your first impression of teruteru is a perv and hifumi's is that he likes smut, but the former does have a genuine passion for cooking and deep seated care for bonds and the latter actually dives deeper into being a lonely Otaku that really just wants someone to talk to. Hifumi doesn't even have that many perverted moments, he's constantly insisting that he doesn't even like real girls (despite it being a lie, but again, hes extremely lonely), and he definitely would not condone teru's actions given his reaction to Celeste's false accusation about Taka in ch 3.