BOS-CVG is interesting as it hits DL right when they are in the middle of downsizing CVG to a spoke from a focus city.
DL is doing no such thing. It's purely marketing, by any normal definition, it is still a focus city. They've already resumed much of their schedule at CVG and what hasn't come back is business-heavy routes that won't realistically return before 2022.
What will be interesting to see is how DL responds, given CVG-BOS is Delta's second busiest route (5x B717) behind CVG-ATL.
CLT/IAH/MCI/STL/YYZ are not returning.
The only non-hub/focus city routes left are BWI/ORD/PHL/DCA/DEN/SFO/LAS/DFW and Florida. BWI/ORD/DFW/PHL will be gone in a year or two. West Coast routes are probably safe as is Florida and DCA for slot reasons.
RJ85, F70, E135, E140, E145, E70, E75, E90, CR2, CR7, CR9, 717, 732, 733, 734, 735, 73G, 738, 739, 744ER, 752, 753, 762, 763ER, 772, 77E, 77W, 789, 319, 320, 321, 332, 333, 343, 359, 388