Thanks guys! Interesting thoughts here.
My post wasn't as precise as my searches (which were really BRU and AMS focused for end of June departure).
Seems like it may just be a timing/advance buy and non-structural thing with DL.

Unfortunately I am not flexible on dates by even a day, which is causing my pain. I was just shocked that DL was pricing $7-8k and SN/UA come in at $4k.\

May dig deeper in the LHR and/or do a one stop. I've dropped the idea of booking Y