it seems to be a common problem in armed combat training... you want to get as realistic as possible without killing people... but unlike unarmed combat, weapon-based fighting has a lot more capacity to kill quickly than subdue... for example a stunning blow from a blade or club could cause bleeding and lead to death even if the intention was to stun...
what you say about the khukuris is interesting.
Perhaps there's techniques that are less practical? In Chinese martial arts, there's a lot of convoluted techniques and teaching methodology in many of the less fighting-oriented schools. Thus some techniques seen with the saber are absolutely bogus. Thanks to efforts from fighters and the practical minded, Chinese martial arts isn't dead. For example the Yang family broke the saber down two 13 techniques and took out the flashy or superfluous stuff. Also there is some situational things... some targets do not require much force to destroy... and sometimes disabling an opponent with a slash to a weak area is sufficient. Although if you have a slice to his shoulder, why not just chop it in his neck, and ready yourself for the next attack?
Perhaps the khukuri isn't the native or most popular weapon of the Sikhs? Not that they cannot use it effectively, but it reminds me of Filipino martial arts. Some Luzon and Visayan martial arts have the kris and barong in their styles, but evidence of their use in those regions is limited. For the most part it seems every region had its tactics, weaponry, and fighting skills and they exchanged and influenced one another - but the Moro arts in the south were kept mainly in their own families, not to be shared with northern enemies. I wouldn't doubt that a good blade fighter heralding from a Filipino martial art could use a barong or a kris well, but perhaps the nuances and technique specific to the kris would have been better handled by someone trained specifically in its use, i.e. a traditional Moro martial artist. That's not to say no one else can learn it... it is after all just a weapon, it's mechanics can be learned.