Every unit and structure present in the game should have a role. Turrets are first tier defence structures for all factions. If a tier one rush is not stoppable, the flaw is with tier one defence.
One reason is that turrets cost too much, as much as a frigate, when they have less utility than a scout because of their lack of mobility and limited range. Why turrets should cost crystal when phase-capable ships don't is a mystery. If all scouts were made to cost a minimal amount of metal and crystal in addition, and all light frigates a minimal amount of crystal, and all turrets were just credits and metal, that might seem to have more rationale?
Another flaw is that the constructors that build structures are too vulnerable. Constructors aren't even jump-capable ships, and its unusual for construction equipment to be lightly built- a bulldozer isn't a runabout, it's like a tank. Constructor frigates don't have fuel, living space and phase engines to spread out their available armour more thinly.
A further flaw is that there is a limit on the number of turrets a planet can support. Only being able to build a handful of point defence structures before an upgrade limits their usefulness, even if they were much cheaper. A few extra points of logistics added to each planet and available at the first level might help.
All of this could be implemented before more drastic nerfs to scouts, and it wouldn't have much impact beyond very early play. Also, players could still be surprised by a rush, if they failed to take precautions against one. Most importantly, it wouldn't be a return to LRF spam.
The map question is one that merits its own thread. A variety of set maps has to be a better answer than random maps, though? If Galaxy Forge worked properly, then militia could have structures and proper fleets ... after all no-one would try to spam frigates and scouts against the current pirates- very unlike history!