On the gravity side of things...
Gravity: 50% increase in speed across marks.
Gravity Drill: 100% increase in speed (at least, more than the turret so it doesn't have to eliminate turret use). It gets painfully slow across the entire system.
Golems:
Botnet - their HP has been nerfed enough. If it is possible to bring HP back up a little to trade for a DPS decrease, do so.
The 20M damage is by design, right? KOs all fleetships in one hit, regardless of ship cap so it's insanely powerful against low-cap shiptypes in range.
Perhaps it's better to have the botnet more shots at vastly smaller damage, like 330,000x80 per 4 seconds (target: a bit more than average fleet-ship mark-II health). This ensures that the Botnet no longer overpowers mk-III/IV ships, but retains most of its former might against lower-mark planets. It's hard to implement a good scaling on this ship unless we went down to 80,000x240......
I mean, I can park one over a mark-IV planet AI command and score free elite guards forever.
Alternatively, please implement the reclaimed-ships-follow-Botnet Golem rule or maximum reclaimed-ship-cap-per-AIP rule, similiar to how the Hybrids have their escort ships.
Logistics-I. 2x+160 can be a little much in combo with halving enemy speed, although my inclination is to bring up the other command stations a little as well as decrease this slightly. If mk-I can decrease enemy speed by 33% instead...
Spirecraft:
This one need a general re-evaluation rather than a piece-meal approach. They are all niche-use ships, which seems to be the design decision. In practice, I build mostly Siege Towers+a few of Ion Blasters and Implosion Artilleries because I prefer not to overly cheese things.