If the defense of this is harder then FS, why not just do FS directly?
The defense should not be harder than FS-finale unless FS is turned on (or everything else is, at least).
The situation may make it or the FS-finale a better strategic choice at that point. Depends on how far away those shards are, etc.
In the one game I recorded those numbers for, the 30 minute Showdown had more than three times as much Exowave strength as the entire 30 minute FS finale. In fact, it had almost twice as much Exowave strength as the entire FS campaign combined: from first shard to Exogalactic Transceiver including several of the timed Exowaves.
And that's not including the normal waves, counter waves, and CPAs.
Its armor overcoming "max armor piercing" is a bug and will be corrected, btw.
Hurray! As it stood, the GCS basically had 5 times as many HP as listed since only Mk IV and Mk V Spire Rams did more damage.
As for the current showdown state, I disagree that it is not winnable. The problem I see is that it takes a Diff 9+ level player who is playing on Diff 7 to be able to do it. I've tried several games on Diff 9 now, an even with chokepointing it gets crazy. On those occasions when I randomly survive the timer, I can't stop the GCS and Friends from stomping me.
Some ideas:
1) Change the GCSs not to beeline to your HW for a little while. Perhaps wait 30 minutes (to disengage from the network), or until they've taken X amount of damage (say, 5%). This gives the player a little time to recover and enjoy the galaxy with no waves going on. It could also allow the player to take them one at a time, which could be significantly easier.
2) To encourage truly distributed defense, instead of having your 34 times strength wave sent to one system, have that much total strength spread equally amongst all systems that can receive a wave. The Counter-wave could do the same thing, spread among all systems that CAN'T normally receive a wave (or amongst all systems, period).
Tone the Exowaves down a bit, and otherwise leave it alone.
Again, I like it - but not for higher difficulties or serious play. It is so much harder to win over the base game victory conditions that there's no point other than bragging rights. Of course, that's what Achievements ARE...