Its true that teslas DO have slightly less damage-per-second and shorter range.
However, they DO have higher health than turrets, they DO instantly attack enemies instead of turrets which have to turn and aim before they shoot bullets, and they give a nice "blowback" whenever they hit somhing mara-sized or smaller, effeictivly keeping away all smaller aliens from your base. They can also shoot directly below them, unlike turrets.
The best base defense are ones that mix both Teslas and Turrets. Turrets for the majority damage. They should be placed in spots where they will not have to turn around alot to hit the target (i.e, in a corner or directly behind a door). And then think of Teslas as a support turret, keeping smaller aliens out, yet damaging the larger stuff instantly and quickly. Place teslas so they are harder to hit (because they are bigger targets). For instance, with a door a good spot would be right outside the door's path, make it so you cant see them from the other side of the doorway.