So it seems that flexibility is more of an issue rather than power-scaling of the Dark Heresy system?
I don't know if flexibility is the word for it, because the system with its elite advances is pretty flexible... but more there is a limit on how flexible you can be.
Simply put, the hard cap on advancement strikes people the wrong way, especially when they have this really cool character concept, and then as they progress they find themselves having to pick and choose skills and limit their characters not because of simple choices, but because they suddenly find themselves up against a hardcap and having to determine if said skill or said attribute pick is going to stop them from developing their character the way they want to.
And that's even before you start talking about combat monsters and over the top gonzo characters. Its very hard to expand your character in fun, non-combat ways because you have to choose to fight against a hardcap and being useful in the story. Want your character to be an excellent singer or dancer... well that there depending on your class can be minimal 300 exp just to get singing +20 assuming that your class even offers that chance. Get a class that for some reason states that your character never sings, and it becomes an elite advance, and assuming your GM is being generous and charging only 150 exp for the skills, its now 450 exp. That's also assuming you're lucky and all the skills are normally 100 exp. Most of them the initial pick is 200 exp then 100 exp for the follow ups, making it 400 exp for a singing +20. And that's SINGING, which arguable comes into play very minimally in an actual game.
But if you want to flesh out your character you have to take it, but that's 450 exp you're taking away from something else that can be more useful in your average game, aka talents. This wouldn't be so bad with an open ended system, but with a hardcap system it can become frustrated.
Even more so if you want to play a God-type character where your character has every combat talent in the book, has elite combat attributes, AND can make a killer cherry mouse, all while reciting the Imperial Creed... from memory.
Make matters worse is that the Inquisitor's Handbook has the beginnings of power-creep raise its ugly head with the new alternate paths. These paths can be a liability because often then restrict you from taking skills from your original pick without paying +50exp per skill, and that can be a HUGE investment of exp, again taking you owe so much closer to that hardcap with very little return.
So while the game can be very flexible with elite advances... that very same flexibility is its drawback since every elite advance takes away the ability to flesh out your character in meaningful ways, due to a very hard cap.
Which is why I'm looking forward to Ascention, to at least raise that stupid hardcap, and allow me to continue to DEVELOP my character along meaningful lines, and make him 3 dimensional instead of constantly fighting the fight between 2-dimensional usefulness and 3-dimensional living breathgin character.