Citing that law as a reason why the setting that Dioxine created can't work like Dioxine intends it to is weird. It's not like it's a law of nature either (unlike say.. Newton's laws or the laws of thermodynamic). There are plenty of stagnating sci-fi settings and the Piratez setting does seem like a decadent empire. Where XCom is typically optimistic (aliens invade, humans band together, learn all their tech and kick their butts), Piratez is quite a dystopia and nothing progresses much (technology is still generally inferior to alien tech from XCom:EU) besides the gals who are developing stuff very rapidly.
Maybe the Star Gods could develop a new better chryssalid, but it would likely be used wherever the front of their war is, not on a backwater hellhole like Earth, except maybe as a test location. But Earth already fell in Piratez during the first invasion, so they might not be the best to test a new weapon either.
The idea of the church experimenting to create an even deadlier alien life form is interesting and between celatids and chryssalids, they have all the traits they need to splice together in order to make it happen.
The only thing left is balancing it so that it's not weaker (it could be, since if spitting doesn't further the infestation), nor too strong, which seems to rely more on AI than on stats, something that can't be modded but could potentially be played with by someone inclined to alter the code, if Dioxine is interested.
Personally, increasing the aggression values of some melee enemies (reapers especially) so they stop being so shy and go for it if they can bite even only once, would already improve the situation. I've had plenty of chryssalids walk up to gals but not strike, and plenty of reapers peaking out then hiding again behind a fence, where they can be hit by flamethrowers or cannons safely.
