What alien settings are you using?British_Petroleum wrote: They even outrange flame turrets?
Currently mk1 sniper turrets are all you need to defend yourself from early game to end game, and they only cost iron and copper, and they make very efficient use of bullets. If they were a later tech then at least you'd need to use other turrets early on.
Mk1 sniper turrets are not going to last long. I'm only ten hours into my current save and I'm already seeing swarms nearly able to punch through a line of a dozen Mk2 sniper turrets.
I have a feeling you're playing on easy settings. The game needs to be balanced so it is still possible in the very difficult alien settings. Then, with that as a benchmark, if people want less of a challenge, they can tone it down within the settings. But the balance and progression should never be such that it is seriously difficult on "default" settings and physically impossible on "death world".
I'm even doing shameless turret creeping with the sniper turrets, as I mentioned, and it's still quite a challenge. The grenades are completely useless, and the SMG with red bullets is "okay" for small hordes but things are not rapidly getting to the point where I'd just get mowed down instantly if I didn't turret creep. And I put heavy focus on military advancement from the very start.