But that is simply physics, since all firearms are lethally dangerous.
Reality shows that the dangerous weapons are the ones of convenience and concealability… again… and still… and will forever be.
An individual firearm’s lethality, since every single one of them from a .22 Short to a .50BMG can kill with a single round, is not a tremendous concern when it comes to it being chosen for a criminal act. The convenience of using it and the convenience of acquiring it are far larger concerns when it comes to selection.
Unlike the US Military, a police force, or even a discerning buyer with a requirements list carefully discerned from asking good questions online or from the learned folk, a criminal who thrives on acts of opportunity will also use weapons of opportunity. This makes the easiest weapons those that are cheap, available, concealable since what they are doing will certainly bother somebody else, and convenient. Sometimes larger weapons enter the stream from sources like theft, other times straw purchases or other methods of supply make them available to the criminal class. But these sources are trickles compared to the stream of convenient inexpensive handguns in the used/surplus market and theft markets. Convenience
However, by and large the criminal class won’t know a Daniel Defense from Daniel Day Lewis. Unless it was the item of convenience, they have no basis to know. Even if it was an item of convenience they rarely care enough to be discerning. Convenient and deniable far outstrip traits like extreme round count between failures, accuracy, or an over the beach test.
So, rifles and shotguns are inconvenient due to size and cost. This makes them unlikely to be used in criminal acts, not impossible. This also means when used they tend to be unopposed by similar firepower until they run into military, law enforcement, or a prepared citizen resistance. Someone shoots and is shot back at by a handgun because the convenience factor overshadows all other considerations for both the law abiding and the criminal.
This really is simple. The AR-15 isn’t that dangerous in the grand scheme because it is inconvenient to use for most criminal purposes. The only purpose it isn’t inconvenient for are ones so high on the risk scale that the particular firearm used doesn’t matter because the mass slaying of people follows a predictable arc too.
The attack happens, casualties happen, after the initial casualties occur and the remainder have fled the area the shooter either kills themselves, encounters lethally armed resistance, surrenders, or attempts to flee. The firearm does not make nearly so much a difference to the situation as the force differential. The attacker possess and is using lethal force indiscriminately or with little discrimination while the victims of the attack are reacting and unlikely to be able to match the return force. This is where things like concealed carry by off-duty officers and citizens make a significant difference as the time to a matching response and return of force is significantly shorter.
We see the same disparity of force in situations that don’t involve firearms if the victims cannot flee the method of injury. The arson in Japan at the studio that killed 36 is a direct example. Deliberate indiscriminate or wide target force against an unprepared victim set results in mass casualties. Since nobody ‘expects’ to be attacked every moment of every day (minus, perhaps, the hyper paranoid who take very odd measures to counter it) these attacks often result in casualties regardless of any policies in place to prevent or mitigate violence. Violence on this level triggers a reactionary response, not a prepared one. This isn’t a platoon of infantry expecting the enemy to advance into their line, it is an office, a bar, a restaurant, or other public space where violence is not an expected norm. Instead it is a notional possibility and that notion trends towards lesser forms of violence from disgruntled or irrate individuals. A bar is more likely to deal with a belligerent drunk swinging on someone that needs to be tossed on their face at the door than a mass casualty attack. Both are possibilities, but one is a regular occurrence more than likely while the second is thankfully rare.
See MAPS for more.