I do not think that bravery has got anything to do with lineage, caste or the religion that one is born into. It just the motivation towards a cause that a leader or a Guru is able to instill in his protege that matters.
Our Gurus were able to instill superlative qualities in their Sikhs through stirring Bani and personal example irrespective whether the person was a Shudra, Brahmin, Bania, Khatri or a Jatt.
Alas among the contemporary Sikhs we do not have worthy persons who can carry the spirit of Gurbani through personal example. that explains our plight.
But as an optimist, I believe that this vacuum will not last forever. Gurbani is bound to find a target on some highly gifted spirited and energetic soul to carry forward its immortal task.
I agree that caste or lineage has nothing to do with martial quality ,but religion has to do with it.For example is it possible for Jain who has never killed an insect to go in battlefield and kill humans and see blood?