One of the most interesting and faction-defining technologies of the advent rebels is IMO "Wail of the Sacrificed", and between that technology and the % income buff granted by expulsion ti seem clear to me that the Advent Rebels are supposed to be dependent on grabbing and holding high population worlds.
Right now in that regard, every TEC loyal player(and some rebels) with a novalith cannon really ruines the advent rebel player's day.
Wail of the Sacrificed is a very interesting cool new tool in their arsenal, and one they will never actually get to use against a smart TEC opponent, who can simply kill off the population of any world that might be turned into a bomb from accross the glaxy with their superweapon.
The point is, while unstoppable economic damage is annoying on both advent factions(as advent has nothing like the TEC shield generator or vasari kostura canon's ability to easily raid even a back line novalith), it's particularly an issue for the Rebels who have 2 of their strongest late game technologies hamstrung by any TEC player's novalith massacreing the populations of their high pop worlds.
A possible solution:
So I got to thinking, the advent rebels are all about rebirth and Resurrection, so why not rework one of their technologies to include planetary Resurrection stations to help their planets recover from population damage. The obvious choice IMO would be "Cleanse and Renew" as that technology is currently boring, rather weak, and the name is perfect for what I had in mind. Perhaps change it to something like:
Cleanse and Renew: Whenever your planets suffer population damage planetary resurrection centers begin reviving some of the populace. If the population loss is caused by enemy bombardment(including novalith cannons) for every 3 population lost the planet gains 2 seconds of "+1 population gain rate per second". Multiple triggers of this buff add to the remaining duration on the buff, but the rate of extra population gain never rises above 1 per second.
Example: Planetary bombardment kills 36 population on an advent world- 24 will be regenerated over the next 24 seconds. 12 seconds later(so 12 seconds left on the buff) a novalith is fired, causing 150 additional population damage. The remaining duration on "+1 population gain per second" increases from 12 seconds to 112 seconds.
[Comments: this would basically mean that over some period of time 2/3 of any population damage suffered from the opponent would be resurrected. Note in cases of large population damage this would be far from instantaneous(it would take 100 seconds to ressurect 2/3 of the population damage dealt by novalith cannon). While the mitigation percentages of population damage is very high(65%) I believe it would be balanced by the fact that it still takes time for the people to be revived. note with this change, including base planet pop generation, in the 6 minutes between novalith shots a planet could regenerate 145 of the 150 population damage dealt by novalith(2 novaliths could still easily outpace this regen rate)]
Conclusion and possible tweaks:
The first shot of novalith would still reduce max population by 40%, so this tech would far from negate the beenfit of novalith cannon, but this would at the very elast make it less appealing of a tactic to simply bombard the advent rebel's planets down to 0 population. It would mean while they would still only get a 60% potency wail(due to the 40% population debuff), at the very least they could rely on getting a partial strength Wail of the Sacrificed off, rather then the current situation where a TEC player can fairly easily kill the entire population of the planet from a nice safe distance.
Conversely if the ability were too strong, it could just as easily grant 1 second of the buff per 2 population lost rather then 2 seconds per 3 pop lost(so revive 50% of population losses rather then 66%).