Isn't the psyker power Weapon Jinx insanely overpowered for a minor power with an invocation threshold of only 8? It renders all mechanical devices within 50 meters non-functional for one round, and causes one gun within that same range to jam on a successful willpower test by the psyker. With overbleed, one can extend the range or jam more weapons. But even without any overbleed, it renders all mechanical devices non-functional for a round. Suppose the acolytes are fighting enemies in power armor? How many people could even move in depowered power armor? Or who have been cybernetically enhanced? If the enhancements are extensive enough, this power could kill the person itself. How long can you live if your artificial heart stops working? Or Necrons? Wouldn't this power knock them out? Would their teleportation devices still take them back to base? In short, in all these cases, wouldn't this power render such fights pretty one-sided? Granted, invoking this power is a full round action, but what's to stop the party psyker from keeping the enemies immobile or inert while the other acolytes strap melta bombs to all of them, then waiting for the party to be clear of the various blast radii, and then stopping?
While all that is wonderfully true and horribly overpowered, remember that most of your team is also relying exclusively on mechanical devices to do their fighting. Nevermind that if you have a Tech-Priest on your team, it's theoretically possible that even a single round of nonfunctionality could KILL him.
Just because a psychic power is "minor" does not mean that it's trivial. Deja Vu has a threshold of 8, completely wastes one enemy's turn and makes them a sitting duck, and the psyker still gets a half action afterwards. Lucky is a threshold 6, half action minor power that is basically a free fate point. Sense Presence is Threshold 7, half action, and automatically defeats all attempts at stealth within 50+m without even giving the sneaky parties a resistance roll. Fearful Aura is probably the most powerful of the bunch, being a threshold 7 sustained power that can decide an entire combat in one action, allow the psyker to just waltz past any number of checkpoints and guards (as they flee in terror), and doubles as a handy psychological torture technique.
If you roll to determine your homeworld, you have a 25% chance of being from a hive world, compared to a 45% chance from being from an "Imperial" world (which seems to be another name for a civilized world), a 20% chance of being from a feral world, and a 10% chance of being void-born. Logic dictates that, given how heavily populated hive worlds are, with a typical one having a population in the hundreds of billions, much larger than any other category of world, that most Imperial citizens must come from hive worlds. So why do you have a much better chance of being from a civilized or Imperial world, and an only slightly lower chance of being from a feral world?
Simple, while the hive worlds are the most populated planets in the Imperium, they are far from the most common planet in the Imperium, or else they themselves would be unsustainable. A common hive world would need tens, if not hundreds of non-hive Imperial worlds to support their massive infrastructure, taking care of the things that hive worlds literally can't, such as agriculture and such, each of which would have a population of a billion or so humans to support it (depending on what living conditions the planet has, of course). In short, the massive populations of a hive world gets rather neatly evened out by the vast number of other Imperial worlds with a combined population that would easily rival that of the hive world.
The number of people on a Hive-World? That numbers in the hundreds of billions. The number of people who are allowed to leave that Hive-World? Maybe a few million. Everyone else is essentially a slave, an overseer or an under-hiver.
Why does a non-psyker get a psy-rating of two from taking the sorcerer talent, and another two for master sorcerer, but a psyker only gets a psy-rating increase of one for each? Why would learning sorcery be less powerful for someone who is already a psyker? If anything, you expect it to be more powerful.
A character that has already studied the arts of the Psyker has far less to learn from studying the arts of a Psyker than someone who never knew anything about it at all before.