It doesn't matter if it's not the same type of damage or if the laser is way stronger.
My point is that Zeus is phasing through Ulti and what's damaging her is the massive lightning bolt. It's electricity.
It has some external damage by burning in the same way that Kaido's boro breath has, but the bulk of the damage is done internally by the electricity coursing through the body. It can't really be called an external finisher when there's barely any brute force to it.