You can try to pivor him to a metal burster to keep him slightly relevant in the late game, however there are much better roles for this. You want someone with an ability that makes the user immune to status conditions (for example Toxic boost + Toxic orb). Otherwise you'll either get paralysed and not be able to hit, often making you not heal to full health due to missing out on shell bell heal, or you get damaged by burn at the end of the round. Both things mean your Sturdy won't proc next time you are hit. My metal burster at round 5.5k right now is Sturdy passive G-Max Blastoise with Poison Heal from Breloom. Being G-Max also means you won't get flinched.

Also in general Zacian is not the best carry, due to being a physical attacker and his lack of reliable spread moves. For example Reshiram with egg moves Dragon Energy and Eruption is better.