until the spawning of reinforcing ships is in some way proportional to their shipcaps- eg, spawning a shipcap=15 ship costs the same as spawning 6x shipcap=90 ships (or is 6x less likely), the AI unlocking low shipcap units is always going to artifically up the difficulty.
Thankfully, they do. If a unit has only 1/2 the ship cap of the "normal" ship cap, then the AI will only be able to spawn half as many of them under the same circumstances as if they tried to spawn a ship with a normal ship cap. There are a few exceptions to this ratio(currently, neinzul ships, bombers, and frigates), and as noted, a few ships do have a hard cap, but for the most part, ratios are obeyed by the AI.
I think the real issue is that the Spire ships have like a .05 ship cap compared to the norm, but have power more along the lines of a ship with a .03 ship cap, thus, even with their absurdly low ship caps, a ship cap of them is overall more powerfull than a ship cap of other fleet ships. This most certainly needs to be tweaked.
Also, although ship cap ratios are obeyed by the AI, ship build times are not. Say the spire tractor platform has a max of 5 the AI can use on any one planet (this is on top of the normal massive penalty they have on thier spawn rates). Fine, that can be dealt with. But the AI can get almost all 5 of them in a single reinforcement. Thanks to their ludicrously high build times, humans cannot spawn their 3 or whatever anywhere near as quick. In other words, the AI can rebuild them much faster than the "build time to averager build time" ratio wold imply, making the early game (when this ratio very much matters) unnessecarily tough. Maybe a max number spawned per reinforcment cycle, in addition to their hard cap, needs to be introduced to the Spire fleet ships. (And also maybe, the Z elec bomber, the Z sentinal frigate, and the sniper ship, as they have similar inflated stats)
EDIT: I am not saying that the AI should obey build times, that would be silly. But just as the crazy low ship cap fleet ships have a hard cap on max numbers, maybe the crazy high build time fleet ships should have a hard cap on rienforcement
rate.