[@Flamelord]

SG teleportation works pretty much exactly like 40K teleportation. Altering something's location in space through unknown means (in exact science, that is). Small tp doesn't use the Warp in 40K. 

Your tp needs a counter. It just does. Because otherwise it allows you to instantly destroy any enemy ship, with nobody possessing the ability to counter it. Instant megaton nuke to the face is hard to outmatch. Hence, a teleportation-blocking Void Shield from 40K aught to block teleportation from the Goa'Uld as well. Alternatively, I could state that the Imperium can also use their teleportation unlimitedly, and tp a Cyclonic Torpedo (world-destroying weapon) to Ba'al's personal quarters. These things are not allowed not necessarily because of fluff reasons, but because else it's just ridiculously overpowered.

However, I do not want to no-sell your faction's abilities. Just prevent them from possessing the power to one-shot any other faction. So how about you can teleport anywhere except where a specific teleport-blocking effect is in place. So you couldn't tp a bomb right into an Imperium ship, but you could tp it right next to it, or at least right outside the forcefield. This allows you to do some damage, but prevents you from one-shotting everything you fight.

There's a reason that characters in shows like this are plot-convinced not to use their abilities to their maximum potential. It's the only thing that keeps them from instantly winning.

Oh and on the Psyker thing, their Space Marine thing IS guarding the Imperium. On the whole no more than 100 space marines are deployed at any one time. Right now is a high-stakes time, and still only about 150 are deployed, out of a thousand.