Ok, so it seems Fallen Spire stuff creates a more-than-usually insane Showdown response. Has anyone tried Showdown without any superweapons at all? No golems, no spirecraft, no FS? It may just be that the bonus the Showdown response gets for Fallen Spire is too large.
Yeah, back during the beta I tried the SD a bunch of times. When you play with no superweapons, or with only 1 active, the Showdown can be difficult, but it is entirely reasonable. You just need to prepare. The Final Exo is the only one that even might include an H/K at that level, and the smaller ones might not even include Golems. Yeah, quick check says the Final Exowave in a no-superweapons game was 150,000 points. Not 90,000,000.
FS seems to be the unbalancing factor more than anything else. 114 systems worth of FS? Yeah, crazy multipliers there.
Did you try cheating? Spawning a few thousand Golems + Spire Rams + SuperForts might help you live long enough to get to the Final Exowave. I'm really curious, since I think that should end up being 10 times the points of the small Exowave. The Large Exowave is 2x, I think. In any case, I'm pretty sure you'll end up with more Motherships than fleetships in that galaxy.