Update: I won the game.
Some more warheads were involved, but it never went into escalating spiral, fortunately- once the third and fourth cities were up, the increased spirefleet strength and the reduced wave size (Due to them interrupting the reinforcement redirection) flattened things out. It was still hitting harder than the fallen spire plot itself over time, but much more often, which was easier to handle.
(P.S. Zombard filled homeworlds are horrible. Especially with a grav reactor, cpa and wrath lance in the middle of the gravity well, on the far size/ holding the zombard blobs. Also, speedboosters+spirefleet is insanely awesome.)
