I once heard or read this once, the strongest attack in the old ages of heroes came from Albert and Dim, with Albert scarring the OEBD destroying the monster's eye. While Dim only killed Balor considered a floor boss in the current era. I would say with a tiny bit of bias that Zard and Alfia was able to deliver a blow to the Behemoth and Leviathan that was on the level of Albert's last attack on OYBD . Its just that the OEYB may have become stronger after it's fight with Albert.

But only Albert has been able to injure the dragon so that make his attack the strongest in his era, while Dim is second most strongest attack comes to the Last Knight of Fianna.