For the heck of it I tried searching for 2 Business Class seats from DTW to CDG next Jan 11 with return Jan 18. I clicked on the box saying I was flexible with dates. I did not specify Delta flights only. I got the calendar back and virtually every day in January had seats available at the low level. On Jan 11th it was for the Air France non-stop from Detroit.

I did not go further and actually try to book the itinerary. I suppose it could be the Delta search engine was wrong - but it sure appeared they were showing Business Class seat availability on Air France.