Ok, 2 diff 7s and no normal waves does lend credence to a difficulty complaint
I'm assuming you're on 4.033, which is 3x easier than 4.032 for this stuff. I'm also assuming you only have one human homeworld; more than one jacks stuff up too.
And the second city won't actually double the size of the attacks, it just roughly doubles the rate at which the special attack "counter" counts up, so roughly reducing the time between the attacks to 1/2 what it is now. Also bear in mind that the interval between attacks increases by roughly 25% each time (as does the budget for the attack).
Another thing to bear in mind is that the Spire really aren't trying to avoid antagonizing the AI; if you use your special Spire ships offensively expect the AI to notice in the form of accelerating the special attacks somewhat. I'm considering removing or at least greatly decreasing the difference between defensive and offensive use, since I don't want to penalize the actual use of the things, but I want to firmly establish the concept that the AI takes the concept of a full-blown Human-Spire Alliance
very seriously.
I think I'll knock down the special attack buildup rate a bit more, and just remove the offensive-use multiplier for now. This may make it too easy for the first city, but that's ok by me considering that it's basically where the game tells you "you might want to stop here". Adding more cities will make things more interesting