Well, I have played in 4 DH Groups and read some feedback on this forums and the consensus in my perspective was that primaris psykers and vindicares are considered game breaking. The Tech Priest might be consindered as very strong though not that absurdly strong as psykers or vinidcares can become.
Let me point out the problem of the Vindicare:
With a roll of 20 he has a base agility of 40 that can be further improved depending on background package (or be brought up to 40). So I take only the 40. With characteristic advances we get additional 30 agility so we have an agility rating of 70. Now add Dodge +20 so we have a Dodge Rating of 90. And last but not least the characteristic Vindicare Armor adds another +10 to Dodge. What do we have now? Yes. Agility rating of 100. This is a ****** auto sucess on dodging.
But hey, he has the Strep Aside and Temple Assassin Trait. Additionaly he has unnatural Agility. So what will this do? Well, unnatural Agility doubles his Ag Bonus to 14. This means with his standard reaction and step asside the Vindicare can dodge 16 times EVERY TURN. No enough he does this on a 100 test which is an auto sucess unless something reduces his agility and even then it would be around 80-90.
And now the problem of the psyker: (Take all the Talents into account that let you avoid psychic phenomena etc.)
For this example I take another roll of 20 for WP, this results in 40, additional 10 for background and we have 50. Take the +30 from the attributes and we have ab WP of 80. and therefore a WP Bonus of 8! Now take the soul killer power, its range will be just 40 metres, not impressive. But now the Damage will be 1D10+32 (For unnatural x2, though you can even get x3 that would 48 damage per ATTACK) the fancy thing is this power ignores any armor (unless it is warded) and can not be seen. The nice thing is for every 10 degrees of overbleed you get another attack with the same profile. Nice isnt it? And with 10 power rols at your disposal it is nearly guaranteed to reach 150 damage every turn as long as you realy want to kill someone.
But hey, lets stick to Dark Heresy and look at force barrage. 1d10+16 (x2) or 1D10+32 (x3) damage per bolt. But hey, its a barrage! But hey, for every point of WP Bonus we fire ONE of this Bolts. So 16 Bolts guranteed. But hey, with overbleed we can create even more! Lets take the 10 Dices again. Lets sav everyon hits a 5, exept one that hits a 6. (And again I am not takin anything into account that lowers the threshold!) this results into an overbleed of 30. So every 5 points of overbleed another bolt! So for x2 this would 22 1d10+16 attacks you can distribute on a whole squad of imperial guardsman. Squad-Wipe guaranteed. But hey, on x3 its 38 attacks!. You can kill a whole platton in 3 rounds without any dodgable AOE!
And now tell me how unnatural characteristics are not overpowered and broken? The core rulebook was written without takin Ascention into account. It was never designed to give unnatural characteristics to characters or increase their attributes by another +10. Its broken, simple as that. Dont improve it furthermore.
PS: I just did the math, with a perfect power roll (10, 10s in a row in addition with ivocation) a full maxed psyker is able to deal 768 Damage in one turn(w.o. ivocation) ignoring any unwarded armor.
The next konventional damage source would be this:
A tech-priest in terminator armor, the muscle implant, the ascendent carrer, heliot device, bc thunder hammer, implanted weapon, full characteristic with lighnting attack would deal 56 damage and 12 pen per attack, with lighning attack (and the missing 4 dices as RF) this would be 208 damage per round.
So a tech priest can kill one greater deamon (100 wounds) per round and the psyker six. (Note the rules for distributing attacks have been taken into account and 3 LAs cant split they damage equaly)
Take into accoun that these numbers are examples for absolute munchkin min-maxer characters but at least they show the power pontential and how it is distributed between the classes.