I find it interesting that you say Farah can not, and has never been able to run under 12.0 in the 100m. He can run 12.5 per 100 in the past lap of a 5k, albeit slow. There's a possibility that you are right and he can't go sub 12.0, but I find it unlikely. I'm sorry if you're under the impression that sub 12.0 is fast, it's really not. I think you would be very surprised how many average runners can run under 12.0, let alone elite distance runners. I have run 49.4 and 1:53 ane I can run 11.0 with a rolling start. With a standing start I've done around 11.5.
12.0 is not fast. 11.0 is not fast. I0.0 is fast.
I'm sorry you can't break 12.0, but I'm rather certain Mo Farah can easily