Last night I watched my DVR'd episode one of FOSSE/VERDON, then watched episode two "live", but by the second half of that one I was falling asleep so I'll have to rewatch at some point. I agree that it's ludicrous that real dancers weren't cast, but Michelle Williams as Gwen Verdon is such a winner otherwise that you could just call the series VERDON or switch it around to VERDON/FOSSE and it would make sense thus far.
For me, the time jumps in these things often result in an irritating moment of "hmm, now where the F are we?" before I've settled in to the scene taking place. At those times it's a distracting gimmick. But a purely linear presentation wouldn't be so compelling either. How about the writers try meeting us halfway on this kind of thing? Agree about the little ALL THAT JAZZ imitations being excessive, and so amusingly pedestrian in comparison. BK and others have already pointed out the anachronisms, a couple of which are so glaring you have to shake your head. But I'll be sticking with it, just as I did with FEUD. Oy!