Interesting concept.
I would have thought the increments of 25 was due to "laziness" for lack of a better word, and to easily differentiate between the skill levels of rookie, pro, all-pro, and all-madden. Simply in an attempt to dumb it down for the masses. I believe majority of their "testing and tuning" would come on default 50, then tweaking under the hood in regards to difficulty levels.
The penalty sliders for example don't appear to be tested at all, let alone in specific increments of 25, as they simply don't work as penalties. Also pass blocking slider for example. Many are now sold on 0 being the best setting as oppose to 100, where as run blocking is quite clearly the opposite with the higher the slider the better the blocking. It's all very backwards and inconsistent and mystifying.
I wish you good luck with it but, and hope you come across something ground breaking.