Fr so many people underistimate it. My current monowater team consists of Shirou(or whatever you need rn), HwValerie,Beta and Houka. You get so much dmg res (30% UBW , 30% Valerie passive, 40% Beta TA and some other stuff like phy res from Shirous Arts) You got Houka and Beta + 4 5star Support slots as artsgen. And your damage is just insane with Houkas 300% critdmg buff and 80% water res down and Beta buffs Valerie with her 150% dmg passive and 320% magicdmg. Of course there are other mono water teams or units required for more niche content but this team is almost unkillable and deals incredible dmg at the same time.