An attack from Gear 5 was already devastating to a giant like Kaido.
People don't understand how dangerous Gear 5 is. It's all of Luffy's abilities in one form.
His
Bajrang Gun is using the high tension and increased power of Gear 2, with the gigantism of Gear 3, the even higher tension and immense Haki output of Gear 5, on top of Adv CoA + Adv CoC, + the added strength and durability bonus of a Awakened Mythical Zoan, which can also alter reality.
A Red Roc from Gear 5 would just be devastating. I thought Luffy might have some limits to Gear 5, but if he can go into it this easily, then he really is a nightmare to deal with now. Fits since he's a Yonkou.
