It does, and like all stats above 255, the returns are diminishing. So, 20% extra defense means the difference between a 735 attack to a 730 damage attack. Non consequential if you have 9999+ HP.

With my Excalibur, I just recreated the conditions and abilities on Caladbolg. The only thing I can't get is it to do 99999 damage to Nemesis, despite 255 in Strength.