I am aware that every Grey Knight is a psyker, yes. So you've got what, less than 400 psykers of no particularly noteworthy ability? Oh, and they can't be doing Space Marine stuff, because if they were doing space marine stuff then they wouldn't be able to do psyker stuff like preventing infiltration. 

As for the teleportation, why? SG teleportation doesn't work like WH40K teleportation, so unless the Astronomican is blocking sensors (which would screw with more than just Goa'uld teleportation tech) or something then they have no real defense against it. 

Only two factions have defenses against teleportation in Stargate, and one of them uses Organic Technology while the other is literally a copy of a superadvanced alien race that seeded all life in two galaxies. Other than that nobody does. the reason there is still a series is because the Goa'uld don't get that technology until late in the show, and because they are too megalomaniacal 90% of the time to do the smart thing with the tech they have. Besides, if you nuke all your opposition (assuming you don't beam the nuke into a wall or something) then you can't have them serve you as slaves, now can you? They're just making an exception in the face of an existential threat. Because y'konw, someone has threatened to genocide their entire species, multiple times. 

I mean, I only have a problem with it because you're just saying that you can straight up no sell anything I do in the area that is specifically a strong point of my faction.