I wil start with saying i really like this game. But in my openion defensive imporvments are curently not worth building.

1. They take up waluable building spots. I think its better to build somthing that produses somting on those spots insted of "wasting" titles.
2. If you are pushed all the way back to your plantets, you are most likly loosing anyway. And if you are not you can focus on killing the transports, escorted or not.
3. The AI seems to be cripeling itself with building a lot of this imporovments, efectivly hurting themself.

I got some ideas for making those improvments better:
- Mabye give them bonuses, somthing like + morale and + pop growth on the host plantet.
- Or Mabye let those imporovments be build outside of the normal titles on the planet. It wil still cost to build them and they shuld have maintenance but they wil not hurt the planet that bad in the long run.