Christian Thibaudeau has a very interesting article about that :
https://thibarmy.com/16516/
He says that he can zercher more than what he can front squat and that it's also the case for other coaches/clients. He raises some other good points too, definitely worth the read.
Interesting.
I also note that I have never done Zercher Squats. I've only ever done Zercher Deadlifts, which has a greater ROM than the squat given each rep starts off with the bar completely on the ground and ends at the locked out squat position.