Delta has been pushing lots of short connections like the OP's (from hubs and/or large markets to long haul) in Seattle for a while now. The fact that they haven't adjusted schedules suggests to me that they're happy with the arrangement. Furthermore, I'm guessing that they do hold HND, ICN, PVG, etc in cases where one of the feeders is running late, but not egregiously late...they presumably
​​​​prefer getting passengers on their way instead of having to reaccommodate them.