Honestly, I feel a bit disadvantaged because I couldn't fathom this question was about BRINGING out the contrast. Grammatically, "have reduced" and "have raised" are perfectly parallel and alright.
I don't deny that C is a more elegant construction - once one has understood the guiding principle - The shift-work equations have reduced X, Y, and Z while raising productivity ..
Raising productivity is active Voice -- while establishes a sense of timing which essentially brings out the contrast -- during the time that fatigue etc were being reduced the productivity was being raised and so on...
I guess with a fair bit of practice alone can these intricacies be understood...
This question actually reminded of the "growth of rail roads led to the abolition of local times DETERMINED by (blah blah) and DIFFERING from city to city etc....
Basically involves establishing parallelism between Past Participle (have reduced) and present participle (raising) ....Not very intuitive but a very powerful concept.