What's driving the pretrial detention numbers is not mandatory minimum prison sentences but practices that lawyers have adopted and the practice of the courts granting double-time or triple-time credit for pretrial custody. That is a significant issue that needs to be addressed. In my opinion, this will not drive that any higher.
As you indicate, a person being up for a second and third time within ten years is a pretty rare kind of situation. The impact will not be as significant as you suggest, but what it will do is keep those very dangerous individuals in prison for a longer period of time.