Aliens have a massive amount of defensive options already.
I actually want to see something more for humans, because all human bases are essentially identical except in placement. Aliens can decide if they want barricades or not, how many trappers, how many hives vs. tubes, etc:
Humans have very vanilla defenses.
I'm not sure we're talking about the same game here.
Let's see, very effective insta-kill turrets for dretches and basis, very effective teslas for larger stuff , and of course the camping horde.
3 very effective ways of base defense.
Aliens, while having a lot more options, are only effective against a loner or two and really dont do much against mass-attacks to base. Camping aliens don't prove to be too effective defense wise due to the fact that aliens are not equipped (or meant to be equipped) with range weapons thus die in masses leading the hummies to s3 fairly quick.
The best alien defense, in my opinion, is a base-sitting tyrant combined with a few tubes and hives, maybe a well placed trapper if funds permit.
Alien defenses are very good at "softening up" hummies for defending aliens, yet they lack the speed and power to finish them off by themselves.
On a side note, since I stopped playing on AKKA, I've realized how well balanced the game really is. Playing on a 24 slot server isn't really the trem way. On a 14-18 server, skill and luck rather then spamming are the key to a good game on both sides.
Stay away from latge servers and your issues with balance will fly out of the window real quick!