Which clashes with the design of the devs - they do compose gameplay elements and story-telling elements together, and if you would suddenly have a common enemy type with near-impervious skin unless your weapon is thrice blessed, without a certain explanation, you would not be fulfilling certain design goals.
I don’t know what these are in specifics, but I seem to have a good guess at they might be; say by one of FS directors - Viktor Magnuson - answering on his interview with Jeficus - i.e., that they - FS - want to make the best melee-combat based game on the market, and that statement has some implications to what’s in the game and what the devs have already worked out.
And let me use a more graphic example - if your thrice blessed Power maul on Ogryn is not wallopping a Groaner - a basic enemy - across the room with a power attack by the virtue of the maul being thrice-blessed-but-not-specifically-against-weak-as-heck-dudes, then you are not telling a story Fatshark wants to tell. That is why I’m disagreeing on the “complication” front.
I don’t see this holding ground with people frequently picking between Flak and Unyielding, rarely Carapace and sometimes Maniac; with ranged weapons following largely the same rule, only with Carapace being rarer - on top of most ranged weapons being trash against Carapace unless rending is involved. Which means that basically 4/6 options are usable; and I could see someone making an argument for taking Unarmoured on certain weapons (easier bomber kills) or Infected (easier dog kills over distance; albeit very niche/dogs are weak to melee attacks). Let’s expand on this in the next take:
FS will not do it, because the current values were tailored to the game since the very release (even with “old” enemy health values in mind; some of these are, dare I type it, weaker than they should be right now /nsrs). Changing it now - alongside many other things that would involve certain and possibly many things being weaker against certain types of armour according to your idea, is risky. Very risky. Fatshark doesn’t do risky - they or any other company cannot afford losing people playing their game to risky changes and reworks. Pissing off potentially a huge portion of Psyker community is not ideal.
Also, what would you do with weapons that inherently do not support Soulblaze - which is basically any weapon that isn’t Inferno staff? If you don’t have a solution for that, making soulblaze weaker on say, Voidblast staff, is also very risky, because you may just kill an entire playstyle - this is an effect enabled by a blessing, and weapons only have two of those.
People are sometimes also taking Carapace on Flamers - and this alludes to another frequent balance dispute, about Uncanny strike blessing passing its global rending value to other effects, such as DoTs, which ignores the only inherent weakness of DoTs (bar Chem toxin).
Say you make the base damage or the ADMs of Soulblaze weaker - it will not matter if people will exploit Uncanny strike still, unless that is also changed; and changing just US is fairly smaller in scope and very impactful, but also very necessary to reign in the silliness of Inferno’s power at present. It seems more appropriate than fundementally reworking one of the Damage-over-time effects that defines an entire playstyle of a class, no?
My reply also has limited scope of which parts of your idea it debunks, but the two main counter-arguments to it I have already brought up indirectly - massive reworks are unlikely to happen due to consequences for the game’s lifecycle and/or support, and story-telling elements will be fundamental to the practical design; which unless satisfied, probably won’t happen, either.