Worse than Kokoda?
Kakoda was a walk in the park for our tough Aussie Diggers ;-)
Worse than Kokoda?
Yes I agree the definition of fierce is very subjective. Perhaps the following criteria could be considered: intensity rather than protracted, hand to hand combat, proportion killed or maimed, proportion killed or maimed in relation to the population of the country.
If defined in these terms, how about the battle of Cannae where the Roman infantry was surrounded. In all, perhaps more than 75,000 Romans of the original force of 87,000 were dead or captured. I believe that the slaughter on a single day was not surpassed until the Somme.
Bulldog
Not long ago a study discovered that large proportion of soldiers lack the courage to kill and so deliberately shoot to miss. How they deduced this I am not sure, and I am rather skeptical of the conclusions. However, even if partially true we are faced with the possibility of two sides deliberately shooting over each others heads in a sort of pact. There is no doubt that in Christmas 1914 British and Germans downed their weapons to play football and invite each other into their trenches to swap gifts.
Contrast this with the Russians in WW2 who placed any 'cowards' on a suicide trench at the front to take the sting out of the charge, and shot them if they came running back? I also doubt if the Germans and Russians allowed medics out into no mans land to tend to the wounded. At Culloden the British deliberately bayoneted the wounded Jacobite's after the battle. So we are left with battles in which if you are wounded there is little hope of survival, this sounds a lot tougher than the former examples.