Brain of Cthulhu
Welp, this solved my problem, good suggestion on the hoik track vs the delay between pillars. I'm not sure what's going on, but the dragon certainly doesn't seem to be having trouble killing things in a timely fashion, just with not clearing the pillars fast enough. It's doing ~ 1.1k damage per hit, averaging around 6k or 7k while eating things. Maybe that's lower than it needs to be but, heck, this'll do as far as I'm concerned.
It brings me back up to close to 500 health after each pillar, which is enough that I no longer have any problems with dying during my test runs. I rerouted some wires, notably the green one, and added the extra teleporter that drops me onto the hoik trigger and runs me to the far end, then on to the next farm. I should probably add an extra set of green triggers above that bottom right teleporter platform, just for safety, but it works pretty fine so far.
Looking good - the hoik along the ground makes a lot of sense since so many hearts get dropped there, and the delay before going to the next farm is minimal. You might end up getting hit by hallow mobs along the way, but the hearts you collect will most likely outheal that damage greatly. This is a nice alternative to equipping health regen items.