It's a question of the rather meaningless number of kilograms and how practical each system is.
To me a weight-based system is much more practical, however obviously it is not as cheap in terms of excess. But it does make it a lot easier if you have multiple bags.
I am not sure how you can say the number of kilograms is meaningless???
With significantly less kilograms allowed there is an obvious drop in the number of bags you can carry also isn't there?
I can see the benefits of a weight based system but not if means an approximate halving (or more than half in one case) of the total weight allowed. I may not always reach the 96kg maximum for many of my flights but I often carry two bags that weigh more than a total of 50kg on a longer trip or if shopping is involved...