[Q]

Baron I repeated a similar combat as you described: An attack with telekinetic projectors 2400kT damage/combat turn on a planet with 20 large weapon platforms. SE IV Version 1.49.
It took anout 20 turn in tactical combat simulation until all weapon platforms were gone. No damage to facilities or population as long as a single weapon platform was intact. After that population and facilities were destroyed at the same time (more damage to the facilities than to the population).