This seems like this might have been an unintended outcome of allowing psy powers to grant you unnatural stats
Warptime (or Protean Form for the really horrific version) potentially grants a lot of unnatural WS and/or BS
Crushing Blow adds 1 damage to melee attacks per 2 points of WS bonus or fraction thereof, Mighty Shot does the same thing with BS for ranged shots
If I have say a 5 PR and I push for PR 8 on Warptime to get +8 unnatural WS and BS, that would theoretically mean that I would gain +4 damage to those attacks if I have the matching talent (CB/MS)
Normally, things like this would grant a bonus to those tests, and thus NOT be counted as stat bonus. The +20 Strength from Power Armour is a good example - it adds to final value after all other factors, but wouldn't let you, say, qualify for a talent with a Strength prereq that it didn't otherwise meet. There is an implied order of operations as to what order things are calculated, and Unnatural seems to be toward the beginning of that equation.
Psy powers that give Unnatural Characteristics seem to screw with this, and can get out of hand in a real hurry once the PCs have some xp under their belts (my current group is at ~30,000xp, they're naturally going to be powerful, but some of this gets a little ridiculous).
Now, going out of your way to create such combinations would be munchkin, but what happens when you can't help but trip over such combinations? The Tzeentch Psyker in our group has his PR maxed out and most of the Tzeentch powers, and it just occured to him that if he were to buy a couple more talents (swift attack, lightning attack, crushing blow), he could use his existing character setup that isn't even designed to be all that good at melee to stack on Warp Time and Protean Form for an absurd Unnatural WS and be able to lightning attack for dozens of hits, each of them doing more damage than the Khornate Berzerker's Hand of Khorne (which is already min/maxed a far amount as it is)
Were these things really this poorly tested that nobody tried making a sorcerer or psyker at higher than like 10,000xp? Did they just not care that things were stacked up to absurd levels so easily?
Worse are the two khornate characters. I have a player with a rune chainsword that ends up doing more damage than when it was a daemon chainsword for no other reason than his corruption value is pretty high, and now it's being elevated to a Legacy Weapon from Tome of Blood. A Legion Chainsword with high Strength plus Mark of Khorne and Synthmuscle, now 8 free damage from being tainted with his current corruption value, and another 4 damage and 4 pen from Legacy, massive bonuses on a swift-attack charge so that Raptor applies to each hit for a full 2d10 is getting out of hand. He's hitting for 3d10+31, Pen 7 each time, and hitting 3-4 times on a charge with that thing, and the other Berserker with the Hand of Khorne is hitting for about 4d10+20, Pen 8 with his oversized fist likewise 3-4 times and he hasn't even added rune or legacy to that thing (I ruled that he couldn't). These are guys with wings or jump packs that are charging huge distances and hitting harder than lascannons while also hitting multiple times. The two of them can demolish a Leman Russ inside of a single turn without breaking a sweat, and can do this from 70+ meters away with a charge. Sure they lose a bunch of that damage if they're not charging, but they're pretty much always charging because targets that aren't built to parry just die in one charge.