It's because KoG players have been hard countering Shirainui Grass with a single card called World Armor.
Shirainui has no out to this card as a single copy of it is enough to mess your whole strategy up.
Some KoG players can synchro plus tribute summon like crazy every turn.
What you guys should know is that not everyone have the skills to spam this card's overpowered effect.
Only high level players make this card look broken. During the KC cup, even platinum rank are starting to use World Armor to counter Shirainui Grass, but they are not able to spam it each turn.
I understand such a deck would counter everything except for a Dark Cavalry or Monarch deck but if a World Armor deck is as expensive as a meta deck we will just end up replacing a top tier Shirainui Grass meta by a new World Armor Top tier meta, which I think is not the purpose this anti-meta deck was supposed to have.
Dont worry about it. At some point, i agree with them about shiranui in General.The shiranuis basically had a hard time sending their monster into GY. However, if we are talking about grass, its totally different case since it give player too much advantages on the first turn