1st: Bloodthirsters "weight" a lot more, at least their mortal hull does. We are talking about tons here.
2nd: Ascention is broken, especaily its Psy-Powers. The problem is that its based upon the original Dark Heresy Psy-Powers that have been written without keeping Unnatural-Characteristics and Psy-Rating over 6 in mind. Especialy the Unnatural-Willpower is an absolute Game-Breaker for it works as a strict force multiplier on all these Powers that are balanced for a Willpower bonus around 7-8 at maximum. But suddenly it becomes 14 or 16 or even more and this screws everything. And the example of your Psy-Power is laughable… there are much more Powers that are seriously more broken than that. I made a calculation where a min-maxed perfect rolled psyker has a theoretical maximum of 750+ damage per round. The second best damage i was able to evaluate with an also perfect rolled and min-maxed character was around 250+(Now with Lathe-Worlds sourcebook a bit more). Both characters had been given 10 dice rolls of 10s for their Damage or Power roll though. This resulted in the ability of the psyker to theoretically kill 3 greater deamons (100 wounds) per turn. If you take an averagy psyker that mainly improves his psy-abilites and is no utter munchkin he is able to deal 100+ damage per turn at ease even without ascention. This is making toast out of any climatic boss encounter. Literaly the only thing that might work against such a PC is a Servant of Khorne + Collar but even then the "passive" Psy-Powers can kill such an individual, you just have to throw somethign at them. A Thirster might be to heavy to throw but hey, WPx10kg thats around 140kg, if you have Flesh Like Iron or a Friendly strong enough companion, you can carry around an exactly 140kg heavy block of adamantium to throw at people. Now you have to pass a BS Check (Unnatural Aim for the LuLz) and throw the massive adamantium(maybe you can even sanctify this solid metal?^^) with your force push. That will be 2d10+28 without any overbleed, and if a psyker is forced to take such a desperate action, hell, give them all dices you have enough talents to prevent the most bad things at that xp level.
And what did we get now? Exactly, a roughly 100 years old psyker that carrys a 140kg heavy cube of sanctified adamantion on his back just for the possibility he has to throw it at someone because his 5 other insta-kill abilities might not work, everything RAW (Maybe without the sanctified^^) and the reason why ppl hate Ascention.
Though… did I forgot to mention how a psyker can alone cause an exterminatus and even survive it while he is on planet? Rules as written too.^^