I never really liked that in the Fate Setting Cuchulain was described as an average hero, when you read his source material hes clearly one of the greater legendary fighters. His Gae Bolg ability never really made sense to me either, especially when he should be able to best 90% of other Heroic Spirits through conventional fighting :P 

My only guess as to why he was described as average was because the bar was set very high in Fate Stay Night with extreamly famous legends. In any other war he's a top level ass wrecker, auto kill spear or no. Also I guess his Master was not the best, but still.