Oh? You sure? Sounded like no mirrors to me.
My wording on mirrors earlier in this thread was probably not worth listening to. Let me rephrase my thoughts into something that will actually work:
Disregard the idea of mirrors for a sec. During a CFOP solve, every single one of the 42 F2L cases (one being the solved case) can occur when the slot is in the FR position. During a ZZ solve, 21 cases (one being the solved case) can occur when the slot is in the FR position. This is a fact, because as I pointed out earlier, the other 21 cases in FR position cannot be solved with a y/d/F, none of which are necessary in ZZ. This remains true for any given slot; there are 42 CFOP cases for the BL slot, and 21 ZZ cases for the BL slot. This is the entirety of the point I ever wanted to make: for each and every slot, there are twice as many possible cases in CFOP as in ZZ.
To address the mirrors issue a tiny bit: You are trying to say that the mirrors in ZZ add to the alg count, but at the same time do not add to the 42 cases of CFOP because some of those 42 are already mirrors. Just look at it in the simplest way possible: Take case #1. If the slot is in FR, you will solve it either R' F R F' or U R U' R'. If the slot is in BL, you would solve it with L moves instead. Since you said you said you count mirrors as different algs, that is two different algs for a single case out of the 42 cases of CFOP (and of course, you could make it 3 by solving case #1 in the FL slot with F' L F L'). This kind of thing works for the rest of the cases as well, meaning that the number 42 goes up in CFOP just as the 21 goes up in ZZ. Ta-da, the difference between CFOP and ZZ is much more than 2.
If I failed to address something that I meant to in this post, by all means point it out.
EDIT: Wherever I mentioned the numbers 42 or 21 in this post, that includes the solved case. So really it is 41 cases that actually need an "algorithm" in CFOP, and 20 in ZZ.