Regarding the Doylist argument, it is still possible this aspect was just something they neglected to address, or, alternatively, they toned up the violence in "Force". I have only gone through "Force" once, years ago, and I have not revisited it since, so my knowledge is shaky, at best, but I do not remember anyone being killed on-screen. I agree it is not a fun argument, though, and it is not something I am much interested in pursuing, to be honest. I brought it up mostly to bring attention to the fact many aspects of any given show that arise debate amongst the fans could simply be something the creators did not even think about. That being said, I am merely mentioning this, I am not interested in actually taking this stance.
My original argument was that most attack spells of the Mid school are non-lethal, even if taken without a Barrier Jacket.
Only way to know is if we see those attacks used against someone without a Barrier Jacket, which, as of yet, has not happened. These attacks could be completely non-lethal, but they could also be lethal, just not on a protected target. I am personally of the latter opinion, but at this point, it is not much more than a personal view that makes sense to me. After all, if this was actually answered by the show, we would not be having this discussion.
Now, considering TSAB is big on the policing aspect, it stands to reason their mages would tone it down when going against regular criminals, who should account for the majority of their usual adversaries, and are probably not high-grade mages. As I said, this actually makes a lot of sense. In this particular aspect, I do believe most spells used are indeed non-lethal, but I also think Bureau personnel would have a shoot-to-kill option, if the need arises, merely on account of the fact other magical systems (and even Midchildan, on occasion, according to the examples we already provided) have the capability to inflict bodily harm, and even outright kill. It just seems like a bad policy to not have the option to match your enemies, should circumstances become dire enough, and it would place TSAB at a disadvantage I find hard to explain, given they managed to become so big.
especially considering that most of their engagements must happen in densely populated urban areas and we know that even on the Mid, most people don't have magical talents and cannot summon Barrier Jackets
That is another problem, as well. The sheer destructive power. Again has me wondering if the creator thought this one through. Such an attack can lay a building low (these spells doing material damage is pretty much indisputable), thus carrying the risk of: A) killing the target by proxy, through fall, flying debris, or burying them beneath the rubble (the Barrier Jackets indeed protect from kinetic damage, from what we have seen in the show, but what if the mana sustaining the armour got depleted in the final punch?); B) killing other, unprotected people in or around the structure, again by proxy. And the thing is, these attacks are used in combat, when decisions are made in split seconds, and rely on insufficient data. How would a mage know there are no possible collateral casualties in the vicinity, or indeed if the protection of whomever they are firing upon will last long enough to protect them from potential secondary damage? And since these massive attacks seem to be needed to overpower strong opponents, how would TSAB contain such an opponent in a densely populated urban area?
Considering this potential to inflict fatalities, I find it hard to believe the attacks themselves are non-lethal. Now, this is not an actual argument, I know. A spell could very well be non-lethal, and still inflict massive material damage, but I just find that hard to believe, as a concept someone in that universe had come up with at some point. It is like designing a bomb that could lay a fort low, but spare the garrison. It sounds great, but since one could not guarantee the crew would not sustain massive casualties through secondary damage, I see little point in this. Especially since it drains the energy from the caster, just seems wasteful.
Do note, I am not saying "all Mid attacks are lethal", I am arguing that the high-grade ones, like the Starlight Breaker, probably are, if fired on unprotected targets. One further reason is something that ties in with what you said before.
It is possible you are indeed correct, that they are designed to overwhelm the magical defences, and concentrate on the nervous system of the opponent, but evidently, that requires a lot of power being discharged (when facing a well-protected enemy), and I think most of it is used for bringing the defences down (since in real life, the nervous system itself can be brought down quite easily, without the need for overwhelming levels of energy). An undefended target would get the full weight of the attack solely on their nervous system, and considering the amount of energy we are talking here, I doubt it would be non-lethal. Let us take the example of Vice's sister again. It is entirely possible the injury she sustained was inflicted to her eye's nervous system. It would keep with the idea of the nervous system being the intended target. If we also speculate that Vice was probably aiming to knock out the criminal (which would keep with TSAB's apparent policy of avoiding killing their opponents), this means that a relatively low-level attack, used on a target without protection, resulted in lasting physical damage.
Now, the attack itself was evidently not lethal, even against an unarmoured person, but if a relatively weak attack like that can do this, imagine what a Starlight Breaker could, under same circumstances.
As for the military argument, that is why I phrased it as "having military capabilities", rather than "being an outright military". I also said they are "trained to use non-lethal settings, which would keep with the peacekeeping, policing aspect". Basically, between TSAB being a full-on military (which obviously it is not), and it being just a peacekeeping police force (which I find unlikely), I am taking the middle approach. Most of their staff is probably involved, and trained in, the usual policing duties. However, they likely do have the capability of militarising (and probably dedicated staff and resources to see this through) if the need arises. I am not saying there is a current external threat present in the show, I said "reasonable possibility of an external threat". The universe is a pretty big place, and can not be treated as a single planet, where all the players are known, visible, and within immediate reach. One role of the military you overlooked is defence, to prevent others imposing their policies onto you.
We have not seen any of the administrated worlds possessing their own military, or even police forces. If they did, that would lead to constant clashes over jurisdiction with the Bureau, and make the whole system unfeasible (what if the local politicians or populace want their own forces to take care of certain things, only way this is not a constant issue is if they have no such forces, and instead rely on the Bureau). It stands to reason they look to the TSAB for not only policing the area, but military defence as well.
Now, this all ties in with my opinion of the high-grade Mid spells being lethal, because otherwise, TSAB's best personnel, its high level mages, would be a rather unreliable asset in a large scale crisis (such as a war, even a localised one), and I doubt anyone would deliberately design an entire magical system around this concept.
As for Orusea, it is not an administrated world. There could be any number of political reasons TSAB does not want to get involved. If they did, it is quite possible their fleet alone would be enough to settle the conflict (however, this is just my opinion, largely unsubstantiated, it would depend on the level of Orusean military, on which we know nothing).
If you would like to know what the Mid would look like if TSAB actually was a military with someone to fight, I can recommend reading the Nanoha BetrayerS doujin. Or not, if you don't want to witness the Nanoha canon and ideals completely perverted and defiled.
I quite liked the "BetrayerS", but the approach I am going here is closer to a fanfic series called "Shadowverse". Basically, the TSAB has a department, the eponymous Shadows, who do the Bureau's dirty work (covert operations of all sorts, assassinations, etc.). While not exactly a military approach, it has two elements that can tie in to all of this, and which I quite like. One is the fact TSAB recognises some threats need to be dealt with less heroically (and decidedly un-police-like), shall we say. The other is that Mid magic can be used with lethal purposes. It actually goes into the mindset of the usual TSAB mage (Nanoha), who is specifically trained to avoid shoot-first-and-shot-to-kill, and who, as a result, loathes the Shadows, and considers them no better than murderers. Can be found here.
