Your post is a great summary of why change in the United States is so difficult. Absent a constitutional amendment, which would have no support, or some really reaching judicial activism (like the SC finding AR-15 style rifles are unconstitutional) stricter laws are about as good as it gets. Even then, as you rightfully pointed out, they don't always work.
I think what bothers me more than anything is the selective outrage. Was this an abject, horrible tragedy? Absolutely. Should we be outraged that an unstable 18 year old, with a plethora of warning signs, was able to pull this off when he should have been institutionalized a long time ago? Yes, of course (I'll also point out that his own mother was so deluded that she left her mother, who her son, the perpetrator, shot in the face, in the hospital to fight alone for her life to search for the perpetrator because she believed he couldn't have done it). Should we be outraged that so many children, and their teachers, have been killed? 100%.
But where is the daily outrage at gun violence? In Chicago there were 3500 shooting incidents in 2021, almost 10 per day (chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://home.chicagopolice.org/wp-content/uploads/CompStat-Public-2021-Year-End.pdf).
Detroit in 2020 had "1,173 nonfatal shootings" in addition to hundreds of murders (https://www.freep.com/story/news/local/michigan/detroit/2021/01/06/detroit-homicides-shootings-2020/6563259002/).
In LA in 2021, there were "1,400 people who survived shootings" (https://www.latimes.com/california/story/2021-12-31/gun-violence-los-angles-15-year-high).
And those are just three cities. And, to be sure, some of those incidents were no doubt carried out by AR-15 style weapons. However, the overwhelming vast majority of gun violence in America comes from handguns. "In 2020, handguns were involved in 59% of the 13,620 U.S. gun murders and non-negligent manslaughters for which data is available, according to the FBI. Rifles – the category that includes guns sometimes referred to as “assault weapons” – were involved in 3% of firearm murders" (https://www.pewresearch.org/fact-tank/2022/02/03/what-the-data-says-about-gun-deaths-in-the-u-s/).
While so many innocent people being murdered at once gets coverage, and has all the talking heads freaking out about banning AR-15s and "assault weapons," those weapons are rarely involved in actual murders. Additionally, the rate of gun deaths in the US has actually declined from prior years, adjusting for changes in population: "Despite the increase in such fatalities, the rate of gun deaths – a statistic that accounts for the nation’s growing population – remains below the levels of earlier years" (https://www.pewresearch.org/fact-tank/2022/02/03/what-the-data-says-about-gun-deaths-in-the-u-s/).
Gun violence is certainly a problem, and proactive measures must be taken to limit it. I just find it ironic that certain political groups will rage about AR-15 style weapons when something like this happens, but are completely silent about daily killings of school kids when handguns are the weapons used, like the murder of Secoriea Turner (https://abcnews.go.com/US/wireStory/killed-baby-year-girl-killed-atlanta-shooting-71622608 ), or a 16 year old kid murdered at his bus stop (https://www.wsbtv.com/video/local-video/16-year-old-gwinnett-county-student-killed-waiting-bus-stop/2043470d-6f38-40c5-a0bb-6fefa737a6c0/).
Handguns will never be banned under the Constitution, and laws that limit the ability to carry or use one likewise will probably not pass constitutional muster. That being the case, hyperbole about banning "assault weapons" or AR-15s should be ignored in favor of a frank discussion about how to limit handgun violence. Don't forget, for all the media's freakout over AR-15s (which NoBoDy EvEr NeEdS), it was a pistol attack at Virginia Tech that remains one of the deadliest school shootings in US history (32 murdered and 23 injured).
Banning guns (or regulating them into non-existence) will not happen in America. It's time to accept that reality and move towards a real solution that addresses the actual problem - and the actual problem is not the availability of AR-15s - its gangs, cartels, and criminals.