If that's the case, then Terminate comes in second, with the ability to spot-kill any creature that isn't pro-red, pro-black or untargetable
I will say this about Mangara, the Diplomat though: if you draw just 1 card on average per turn, then it's worth playing in Mono White decks
Pursuing chains like this will also lead to significant creature buffs as well since Chishiro grants a +1/+1 counter to all of your modified creatures each turn
Kona, Rescue Beastie Kona is a card that can do incredibly broken things
There's also a really cool "Earthquake" subtheme going on with Giants, where they pair up with mass damage abilities that kill off weaker creatures
To keep access to that effect expensive, WotC dropped it on a 4/5 flying vampire and priced it at 7 mana