A JV controls capacity between partners (and fares, if they are allowed which is the case of DLAFKL) and revenue sharing. But a JV does not control load factors which depend on actual bookings by passengers. On CDG-JFK, AF has most of the capacity because they have 4 or 5 flights/day while DL has one or 2. Whatever the load factor of a given flight, revenues or losses are shared between the partners for the considered route.

This being said, capacity is indeed to high at the moment on this route. Omicron has perturbed a lot the return to normal, and the maintained need for a Covid test on the US side is scaring a lot of US people to travel to Europe with a non negligible risk of turning positive before returning home. But we can hope this will not last too long and the capacity is here to cope with demand...if oil price is not going too high