Besides being thermally weak, Fibrament's other Achilles Heel is that it doesn't have the conductivity to bake a quick (4-7) NY style pie in a typical 550ish home oven.
I don't know how you can say this. I regularly crank out 2-4 NY Style pies (62-65% hydration) on a Fibrament. When the first one goes in, I start on the second. As soon as the first comes out of the oven, then next one goes in and I cut/serve the first. I run the oven at 525 F with a one hour warm up. I have a 19 inch round Fibrament on lowest rack and and one the top rack. (UPS abused and chipped the first one, so I received another one free) Without the top stone, the bottom is done way too fast. The initial cycle time is about 5 and a half minutes and rises to the mid-6's by the third pie. The pies have the right oven spring, a crisp, slightly blistered bottom and a drooping tip when you fold the slice. The 3/4 inch thick stone dumps plenty of heat into my pies and I have no screwing around with switching between the bake and broil cycles; I just set the bake at 525 F and go. Could I go faster at 550 F? How about getting another 35 F, by tuning the oven setting? Sure, but 525 F cooks them perfectly and about as quick as I can cycle them.
The research that the Corderite has better properties is like comparing a Chevy to a Ferrari, while driving in a school zone. A significant portion of the performance you are looking at is beyond what can be used. I'm not running a kiln, I'm cooking pizza. In the home oven environment, the Fibrament meets/exceeds the requirements. My stone does not see temps above 600 F, is not subject to thermal shock (at least not beyond the very occasional cheese/tomato dump) is not heated unevenly, etc. The Fibrament just provides a great balance; it cooks the bottom quickly enough to provide the right crust, yet not so fast that I have to work hard to get the top done at the same time.
Is the Corderite a better engineered material? In some environments, definitely yes. Is the Fibrament sufficient for a home oven? Definitely yes. The overriding factor for me however, beyond already owning a Fibrament that does exactly what I need, is that I’ve not ever seen a 19 inch full round Corderite stone, which is what I need to make an 18 inch NY Style pie, 'cause as we all know, if it ain't 18 inch, it aint NY Style. <grin>
The one question that keeps coming back to me is, Why don't pizzarias use the physically superior Corderite in their ovens?