Most other mass removal spells in Standard right now either cost more mana, have some sort of stipulation on them that gives your opponent something in exchange for blowing up the board or just isnt as efficient as Day of Judgement
Play Boosters, as the name suggests, are made to play Magic: The Gathering
Sure, Belle doesn't have a lot of survivability, but being able to double your ink output means that you can safely rely on other cards to protect her
As if that wasnt enough, Halo Fountain can win you the game outright
Flying 9/9 Illustrated by Kota Nakatsubo Standard Legal Alchemy Legal Pioneer Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
Three-chapter summons like this are only good for one attack or two block steps, so most of their value is tied into their abilities