Apparently though, these people know what they're doing and wrote their own, specific for software architecture! Very curious to see if it works well.
That's a problem that plagues more generic options like Graphviz or (disclaimer: I work on that) yEd where you get the generic layout options and have to adjust them to make sense for your diagram. More flexible, but also more cumbersome, often with the problem that you crave for manual adjustment if the layout is not quite right.
Layout engines
dagre (default): A fast, directed graph layout engine that produces layered/hierarchical layouts. Based on Graphviz's DOT algorithm.
ELK: Also a directed graph layout engine. More mature than dagre, better maintained (part-time academic research team working on it), with recent releases.
TALA: New layout engine designed specifically for software architecture diagrams.