I agree with most of those complaints about the core system, and can add more:
Weapon power levels make them either nearly useless, or instant kill- both of which are boring results- with very few weapons forming any kind of 'happy medium'. This has the effect of forcing min/maxing rather than encouraging characters to use 'characterful' weapons, such as Kal Jericho's signature twin laspistols- joke weapons in WH40KRP.
I think this is only partially the fault of the weapon profiles (if at all), but rather of the stacking layers of protection that result in a wide range of resilience. Even normal humans in DH could sport anything from 3-14 (not counting Ascension) in terms of damage mitigation, and whilst Pen values helped alleviate the issue somewhat, they didn't remove it entirely (especially as the most common weapons had zero Pen).
With such a large gap, it gets very tricky if not impossible to design weapon profiles that are a threat or at least a concern for anyone without being overkill for some. Of course, the dice-based randomness of weapon damage didn't exactly help either.
This approach really began to show its downsides when Marines were added, though, further expanding the range of damage negation ... and ultimately leading to the designers implementing band-aids such as the Felling trait or Horde rules (which, in their newest iteration, are essentially two different rulesets, treating characters based on their "race", as apparently even the developer now regards the system as being unable to treat characters by the same laws).
There were a lot of good ideas thrown around (and don't get me wrong, the product line saw much improvement in certain sectors), it's just that the overall result was still overshadowed by what I perceive as "legacy flaws" that the studio was either unwilling or unable to replace with something better.
The general thought was that GW mandated certain standard elements, such as a percentile base, which prevented FFG from attempting something true ly innovative, like they did with their Star Wars rpg.
Is that just hearsay based on fans desiring to point fingers, or did the designers really allude to this? The foreword for the DW RPG included a message from GW that included a remark about the FFG team having had "a lot of different ideas" than them, so it doesn't seem like they were generally opposed to alternate approaches (which becomes especially clear once you compare certain background elements in these RPGs with GWs own books).
Of course, at the same time I do not doubt that GW could simply be very inconsistent with what they would decree. It'd fit to other things I've heard from certain authors.