I've not done purely JFK, but my 2019 was:

Week 1 - LHR/ORD (Monday, back Wednesday!)
Week 2 - LHR/DFW (Monday, back Friday)
Week 3 - LHR/MIA (Monday, back Friday)
Week 4 - LHR/JFK or EWR (Saturday, back Friday)

This repeated for about about 3 months,

That was in the days when BA updated their entertainment monthly - although I tended to fly AA for the seat.

The real issue with anything on the East coast (and to a degree the mid-West) is the flights are just too short. My last EWR/LHR was something like 5:40. Even MIA is getting short at 7:30. You just can't sleep,

Then with many of these flights dumping you into LHR at the crack of dawn, you just spend the weekend fighting to stay awake.

I think if I had to do it again, LAX, SFO or SAN would be a lot easier.