User blog comment:ClariS/AD has Diminishing Returns!!/@comment-4087140-20120829030012

This is not diminishing returns. Diminishing returns means that putting one point of X into something yields less and less Y as you put more in. As it so happens, every point of AD/AP always increases the relevant stat by one point; that never decreases, and so there are constant returns.

You're just making the same mistake that others (including myself, in the past) make, which is looking at the overall percentage impact. That's relevant for some theorycrafting, but not diminishing returns.