The thing is it's in their religion. Among their primary beliefs are to fight for the rights of everyone, and to be ready to die doing it. It doesn't make them super soldiers necessarily, but it does make them very quick to fight to the death doing God's work. All baptized Sikhs carry a dagger, the kirpan, traditionally not for offense or even necessarily self-defense, but in case it is needed to defend someone from injustice.
Even the name for a baptized Sikh is a "saint-soldier" and he becomes part of the Army of God. This isn't a figurative army, such as spreading the word or such. They mean it literally, be ready to fight to the death to protect any of God's people (which to them means every human).
The Western soldier will fight to the death, but he is thinking all the way, he is always trying to win.
In the 1980s one of our Special Forces soldiers commented on how his South Korean Special Forces counterpart thought the best way to kill a tank was to leap onto it with explosives, in a suicide attack, brave, but backwards, simpleminded, and short sighted, and the way to lose to a race that fights like a relentless, focused machine dedicated to always thinking, always wanting to maximize gain from the death of it's well trained and intelligent fighting men.
As you know the British soldier often knew that when fighting against some, like the Sikhs or Africans it meant fighting to the death, but we still fight, we are willing to die, but try to avoid it, we are focused on winning the battles, the wars, the American GI during the generations of the Indian Wars knew that they did not take POWs but we still fought and prevailed.
The Sikhs were no match for the Western soldier and we know that from the wars that were fought.
I think the Japanese were incredibly stupid to fight as they did, and I see that simple minded way of dealing with fear, in many foreign warrior cultures.