And your argument only makes sense in the extremely unlikely event that ringed mace had a proc mod for a while, and that proc mod was then was removed, which would have eliminated the "need" for it to be removed in the first place.
http://lucy.allakhazam.com/item.html?id=6607
Notice in the history how it doesn't have a proc mod and hasn't since lucy started? What makes you think it ever had a modified rate other than the fact that it stopped dropping?
Ringed mace was only in for a few weeks at most. Some dev probably designed it and it somehow ended up as a random drop, so they took it out and forgot about it.