There are 3 possible cases ( interpretations) of " other than the sum of the parts":
1. less than
2. more than
3. equal to
We can discount the 3rd for obvious reasons. The 2nd is easily seen around us, which might account for the common 'reduction ' of Aristotle's and Koffka's statement(s). How about number 1?
Can we identify a case where the " The whole is LESS than the sum of the parts?" and it is yet relevant to the concepts where this axiom is used, specifically Holism, Gestaltism, Systems Theory... useful in understanding the universe around us?