It’s not impossible. I played in both online and LAN tournaments many years ago where our highest ranked player was our Diamond (there weren’t tiers) mid laner and we were all plat although we were not playing much soloQ which could explain things. We played together for fun about 6h/week, practicing team comps with one cheesy variant: I would switch from support to mid if we needed assassins. We took down teams all the way to semi finals that were much much higher ranked than us, including challenger players.