I levelled Arash because I was done with the 3* Archers and everyone was talking about how useful he was. Well, he can kill an average wave on the cheap with an Imaginary Around CE (saving your Kscope, if you have one, for other Servants) and since he's useless after that he conveniently vacates his place for you too. He's not gonna carry a CQ or anything, but he's fine as a cheap one-use waveclear.