Eventually decided to skip map 19. Whether it was on crowd-shaping, or sequencing the activations [spoilers](for the second encounter, should I've kept the revenant alive to mess with the viles?[/spoilers], I simply didn't have the skills. I'll probably come back to this level later, because obviously it was designed to make us suffer in clever ways.
Map 20 is pretty amazing so far, but I've found a place when I get stuck (img - stuck after climbing then falling from the small elevator) Nothing much, actually - but I thought it'd be useful to point it out.
Again, using supercharge is really cool. The Diabolists, Tormented Souls and Diet-Cyberdemon really adds a lot of tactically interesting situations.