Hard & soft product are based on the market not what is "fair". There are a lot more people who will pay the premium required for full D1 hard & soft product on MSP-CDG than on JFK-REY. That's just the way it is. If there were a market for widebodies with the latest hard product on the route, DL would find a way to make it work.
On the broader issue, DL is simply rearranging the utilization of its higher end aircraft as the US economy continues on screech. Those new D1 services are using aircraft which used to serve shorter and less profitable TATL routes.