Well, yes, these are all okay points, but I think you're missing something: All of the stuff you listed can easily be done by Sovereigns (who specialize in Craft, Integrity, Performance, Socialize and War). What you really should be asking is, "What do DBs have the Sovereigns don't, or are better at?" In my eyes, though I'd need to double check when I'm not away from my PC to make sure:
- Healing. Sovereigns are decent at curing illnesses, but without notes I don't think they have any method of quickly healing injuries.
- Animal handling, don't have any of that to my knowledge either.
- Stealth: Sovereigns are brightly shining rainbow demigods, they are NOT subtle in anything save for their words.
- Speed in/out of combat except when crafting.
- Martial Arts, so long as one DB is Immaculately trained, they are likely better than any Sovereign monk.
Again, I'd need my copy of the Exigents book to make sure, but these are some examples that come to mind.
Some ideas:
1. Dragon-blooded exalt as teenagers so they have a higher essence (at character creation). This benefits them in martial arts and evocation as those are locked by essence.
2. Dragon-blooded are resonate with jade, the most common type of magical material, and neutral with almost all others. Sovereigns start as neutral with adamant, rather rare material, and dissonate with almost all others, though they can get resonance with an essence 3 charm.
3. If we are going to be near an ocean, sail charms, because we might want an admiral for the navy.
4. To get going a Sovereign need to find a charm that lets them get to 1 anima. If nothing presents themselves, they might have a cap at 4 dice. Dragon-blooded are always in reach of their cap (max 6) and all their excellencies have a little special bonus in efficiency.
4b. Them being efficient is also a good thing considering we are in Warhammer and might not want to have to fight a small village for using magic, when they light up going iconic. If they have to limit themselves for this then the DB would be better at it due to that little efficiency.
5. Generous limit break terms. DB don't have a track at all.
6. Stealth, but also spy stuff. Disguises, hidden codes, hide weapon abilities, a charm that lets them have the wind carry a message miles, having varying aspects that might help not be detected.
7. We don't have to convince a member of the royal family to take an assignment, like we would with a Sovereign. Like spy work or fighting rats.
8. Bureaucracy charms. To help the economy along and improve stewardship.
I would argue that a DB would be a decent choice in all the positions and would be a better underground fighter then the Sovereign due to also having a synergy with the underground and having more direct access to the relevant charms, not to mention trying to convince a prince to spend his time fighting rats or goblins.