Because Ikoku is a penetrative attack while Hakai is an explosive attack
Something you literally pulled out of your ass
Ikokou literally "exploded" the same way Hakai did against Kidd.
Both attacks have same nature cylindrical beam yet one is different than the other??
This is where your dishonesty comes from. You made something up to save face.
Funny thing is if you were intelligent you know it takes A LOT more than half the power of attack to block it for even one second. Hakai would fully diminish Ikokou and it won't even be halted.
And current Zoros defensive power is far above roof top Zoro.
In the midst of that even with your own nonsense Zoro can fully block Ikokou casually. He'd do it even in roof top but can certainly do it now.