https://www.google.com/amp/s/simpleflying.com/delta-air-lines-boston-biggest-user/amp/

Cirium indicates that Delta is Boston's largest airline by flights this June, partly influenced by its growth and also temporary cuts by JetBlue. Indeed, JetBlue was top until last month, as it usually is of course, but its Boston services have been cut by 7% month-on-month.

Not sure how much weight this source has, but that's what i was going by. DAL definitely isn't slowing in Boston