"Psychic defense needs to be ubiquitous if you're going to (pump) out rules like that".
Really when you look at it, recent codices have been stacking up the psychic awesomeness, and Grey Knights are going to take the cake. And they also have good defence: Librarian with a hood is a standard marine defence, but top it off with Aegis Armour on everyone and Stabilization feilds on vehicles that can cast powers, well you have a pretty psy resistant force.
There are 3 Armies I can think of that can decently resist this
1- Eldar. Specifically Eldrad. 3d6 tests on everything, the GK will face more perils than George Bush at the DNC.
2- Blood Angels- Standard Librarian psychic hood, but also the chance to take Librarian dreads, offering more hoods
3- Space Wolves- Able to take 4 rune priests. Which means 4 hoods
BUT those are expensive options. And that is only 3 armies. Lets look at 2 armies that have no psychic defence, but very much should
1- Deamons (besides the Blood Thirster)
WHAT? Why do these armies suffer? The only army that should not have defence is Tau, for obvious reasons. If anything, Eldrad's rule should be an army wide rule for Daemons. And CSM should have something equivalent to psychic hoods.
And these armies are about to majorly suffer at the hand of the GK. With no way to block powers, they will be at the mercy of the new horde of psykers. For instance, it costs 20 pts to Deamonically posses a rhino. Whereas it will cost 5 points to essentially do the same thing for a GK rhino, without the loss of BS. It will only need to pass a psychic test. On LD 10. Which many armies will not be able to stop. Yes, we know CSM are outdated and depressing at this point, but any inherent benefits are about to be trumped by the GK. Hammerhand is a standard power in GK codex. Plauge Marines are the Troop of choice for CSM at T5, FNP. Downside- I3. They will be shredded by S5, Pweap weilding, I4 combat beasts. Oh yeah, the GK are 3 points cheaper. Forgot to mention that. It wouldn't be as bad if the CSM could block hammerhand, but there is no way for them to.
Other armies suffer this too. EG Tyranids should have a shadow of the warp ability, which should be like a table wide psychic hood of sorts.
This new force is a cost effective Psychic army, and their is not much in the game that can stand against their psychic might. So while at a glance, some things may seem fair and balanced, you must remember that who they are facing may not be able to handle the heat.