Preface:
I think it's clear that DP need to be nerfed, but I dislike the suggestion to simply add a saving throw. This nerfs STR based, CON based and CHA based divines without having any effect on WIS based divines. I don't think that is fair because 1) it is a retroactive change, and 2) DP needs to be nerfed across the board anyway.
Suggestion:
Decrease fully stacked DPS, increase ease of use and keep SP efficiency at the same level (e.g., damage per SP spent). This could be done in many ways, but here is a specific suggestion:
Increase DP duration to 20 seconds (from 15)
Increase recharge to 12 seconds
Increase damage by 25%
This will result in a divine punishment that is two-stackable (rather than three), maintain similar SP efficiency, and an overall nerf of 16.7% off of fully stacked DPS.
In addition, it will be easier to use. It will be more feasible to use against non-boss single targets and the cost if a full stack expires due to lag, mobs flying away (jailer, judge) or whatever will be less.