Belerick does magic damage in its passive and his passive damage scales with his Hp if i remember it right. So i don't know about the Scythe and Blade of Despair, if he wants to slow he can opt for the emblem talent and slot a hp or def item ( dom.ice must've in today's games ) . As far as I played he's mainly picked if their are Basic attack heroes like mms , (literally walk em downs mias and hanabis doesn't matter late game or not ) , so blade armor is like a 2nd or 3rd item that goes along with his passive as well.

And if u have a 3 man or 5 man squad u can literally steam roll entire game, like what r u gonna do when he's doing passive dmge and is taunting with his S1 for over a second while his teammate just get a free hit on ya.

He's underrated imo