>>54925218>80/120/80/90/65/135vs
>92/120/115/80/115/138Besides significant drop in Def and SpD, Zacian and Chien-Pao have really close stats. But considering Chien-Pao is an Ice type, even if it had 115 Defenses it really wouldn't be that much different in practice.
Also keep in mind Chien-Pao has better ability (especially in doubles), better moves, 2 STABs, and also more impactful immunity.
Despite all that, Chien-Pao is not a restricted while Zacian-H is because the Ice type restricts Chien-Pao so much. Because it's an Ice type with poor type match-up, even if it had better natural bulk than Zacian, it'd still be forced to run Focus Sash or Boots vast majority of the time. It has to be worried about some of the most common moves in the format like rock Slide or Heat Wave, and also stuff like Mach Punch or Bullet Punch.
It currently gets by because it's the 17 year old in a 5th grade class.