One of the benefits of Gun Reform is that population 'feels' safer (from guns anyway).
The people who had guns will not tend to see it that way, those who did not have will tend to.
The big disadvantage you have with guns over other forms of assault, is that it's rather difficult to run from a gun, or defend yourself from a gun.
Yes, that's the general allure of a gun, its efficacy as a weapon. But that swings both ways, the same reasons it has utility as a weapon for offense makes it good for defense.
The physically weak grant the physically strong a monopoly on force without weapons. As a young person who does not own guns the feeling of safety I would have are different than, say an 90-year-0ld lady who keeps a gun at home for protection.
I bet she would feel less safe without her gun, not more. This is the small cost of gun control but it must be balanced against the small benefit.
If you look at each of the cases - they weren't shoot ups by hardened criminals, but by people who cracked. Those 'people' who crack, now no longer have access to semi-automatic weapons. It's a huge difference, and something completely ignored by pro-gun lobbyists who avoid this significant aspect of mass shootings.
No, it's not a huge difference. If you allow yourself to be dispassionate about it you will realize that it is a statistically insignificant (comparable to being struck by lightning) difference. It is a rounding error of a difference that society likes to overreact to.
Not just because it's so exceedingly rare to begin with but because the majority of mass murder these days already does not use guns (bombs are by far the most common weapon used in mass murder) and even if you succeed in eliminating guns you only reduce the risk from these individuals incrementally, not entirely because guns are not the only weapon for this kind of thing. Taking guns off the table does change the game, it takes certain narratives off the table for one (and in western society the kamikaze or suicide route is not as popular) but it's a rounding error of a difference in the grand scheme of things to just take one of the weapons off the table.
I don't deny the tactical differences guns make and that the elimination of guns will likely reduce the risks of mass murder, but this guy made bombs too, if he had no guns it is possible that bombs would have just been his primary, instead of secondary, attack and there is no magic trick that makes this risk go away entirely, it just is slightly mitigated and when an exceedingly rare risk is slightly mitigated it really isn't that significant in the grand scheme of things and the costs of the reaction need to be carefully considered.
The same sort of people are involved in them in America I believe (people who crack, not pro gun-lobbyists)
So while there is an obvious before & after comparison (which as you correctly pointed out, isn't scientific because of the small pool) - it is accompanied by a change in circumstance of available weaponry for the type of people who commit these things.
I agree that it makes a difference, but even if we take all your data and accept it blindly we are probably talking about fewer people per year than die from shark attacks and we aren't going to go and ban swimming over that. My point is that every day we have risks that are orders of magnitude greater than this that we accept as part of our quotidian ride. These are merely exotic risks that we dramatically inflate the importance of. Just like terrorism, it's a statistical rounding error with disproportionate reactions. But that is kinda the point of terrorism and mass murder, why be played like a puppet? Your safety the day before it is the same as the day after it, the difference is how you feel.
Reality is not binary, there isn't safe vs not safe like our minds try to make rationalize everything as. In reality it's just a sliding spectrum of risk and everyone needs to draw a line somewhere. Remember, I'm fine with banning guns because the cost of doing so is slight in my opinion and I think the benefits generally outweigh the risks. I am only trying to bring a sense of proportion to this debate.
Banning guns will make a small difference in our safety, having guns makes a small difference for the individual's safety (most predatory attacks try to employ the element of surprise and do so devastatingly enough that being armed is moot in most cases outside of home invasions).
In the case of the USA, the prospect of meaningful legislation is so remote, and the chances of effective enforcement also bad enough that I think it's actually not worth trying in the US. Gun control only works if you can "starve the market" of guns, that is next to impossible to do in the US and what it results in is just poster children for the gun lobby (where the legislation is not effectively enforced, and merely does grand a force monopoly to criminals like the gun lobby argues in a self-fulfilling prophecy).
Boycotting the cultural event and denying it the attention that it feeds on will go much further towards improving American security than will trying to ban guns. Attention is the fuel for a lot of these people. Inspiration flips people more than access to weapons does.
This guy tried both guns and bombs, the tool is not the key limitation, the flipped bit is. Guns flip fewer of those bits than a lot of things (e.g. the coverage of this event is going to flip some).