I don’t think mass shootings (or any of the other violent crimes) will improve until humanity has improved their value of human life. You can outlaw anything and everything, make it harder to get guns or drugs etc but people who don’t value your life or even their own will find ways to be destructive.
It is true that there are less/no mass shootings in countries where there are strong gun laws, but I don’t know what other factors exist there. And I can only speak for here, where I am most familiar. I don’t think anything in the US as a whole will change until we figure out a way to change the way individuals live and view their lives and their worth. It has to change within the communities, the schools and move up from there.