I have calmed down from my considerable disappointment yesterday. First, thanks to Frodge for highlighting this problem in the first place. And thanks to everyone who chipped in with suggestions and the like. Whoever posted the FEL work-around has at least given us an option. Wilt has some valid points, above, about other cameras and ETTL bounce flash. All-in-all, I enjoyed the mental challenge of documenting the issue. Thanks for reading along, and for all the encouragement.
Just so you know, I'll be keeping my 70D, too. So far, it does what I bought it for. The AI-SERVO auto-focus is much better than my 6D. The DPAF with STM for live-view and video is still miles above any previous dSLR. Lastly, I am good enough with flash to deal with this (relatively) minor issue and still make decent photos. In the end, I still have a 6D and a pile of nice lenses and accessories.
I considered buying a 7D Mark II. I have done enough reading to come to the conclusion that the focus issues with it are confined to a few copies, and a few users. It is not a prevalent problem. That said, I am not in the mood to give Canon any more money right now. The main advantage of the 7D II is its AF. I don't need that; my 70D does what I need it to do, with the small exception of bounce flash. I am way more disappointed in Canon and the way it is handling (NOT) this issue, than in my 70D.