Just wanted to report additional info without starting a new topic.
At check-in today overheard argument ahead of me, apparently a lady got downgraded from J to Y+ and was very not happy. When it's my turn I asked about how often that happens, and surprisingly the agent said almost everyday as ex-EWR flights are almost always sold out in J class. Also was told usually every flight is fully booked in all three classes.
Looks like EWR is a winner!