[Master Belisarius]

"In my game they didn't build until now weapon platforms, mines or defence satellites even on their homeworlds. "

Looks weird to me. The Pyrochette never will build lots of weapon platforms and satellites, but yes mines and fighters.
But, in the early game, the Pyrochette always build some weapon platforms and satellites (some in the homeworld and some in their first colonies).
Are you playing a game with full tech, right? Maybe they wanted to build those defenses, but they were without resources.
How many staring planets have your game?

Thank you again for your comments Q!!!!