I don’t think turrets need to do less damage - just have a lengthy cooldown and/or a limit to 1 per engy. Lowering the damage or increasing their hitbox, just goes to make them all that more ineffective. Sometimes having things unbalanced in a game, is a good way to balance the game. A good example of this are the heavy weapons in Brink. Prior to seeing them in action, everyone was concerned that they would be OP, and then when we finally got to use them, we found that not only were they not OP, they were a bit on the nerfed side. The higher health/heavy weapon bonus of Heavies, just didn’t compete with the speed and mobility of Lights, and it showed when you played more competitive games, where teams would be consisted entirely of Light builds.
The heavy weapons should have been OP’s - they should have been designed to strike fear in your eyes if you came face to face with one. This “unbalanced” approach, would have helped balance the pros/cons of choosing Heavy over Light. Perhaps this is how the turrets should behave - perhaps they should be deadly, since trying to “balance” their damage could ultimately just nerf them. Look at the turret in TF2 - fully upgraded, that thing is a beast, and pretty much means instant death if you run out ion front of one, yet overall, they feel balanced, and there are ways to counter them. Maybe give them low health, or introduce counters (which SD very well could be doing now) like emp nades. Also, removing the “slowdown when shot” mechanic, would help balance them out as well.
As for mines - I was a fan of how they operated in W:ET. Marked for teammates, invisible to enemies, spottable by covies, and hiss when you step on them, giving an engineer a chance to disarm and avoid damage/death. Now I haven’t played W:ET in a long time, but iirc, you were also able to destroy mines, even if you couldn’t see them. I remember this happening on the last obj on Oasis, when they block the back entrance to the cannons with a minefield - throwing a grenade would clear them out. I liked that mechanic.