I agree that banning semi-automatic weapons is a bit of a pipe dream, but I do believe it's what is necessary.
And (this is not pointed toward you) to all the people who like to beat the "CRIMINALS ARE GONNA GET THESE WEAPONS EVEN IF THEY'RE ILLEGAL" drum ... no effin sh!t. We all know that. But it's too goddamn easy for any joe schmo to purchase one.
Mental illness is one of .. if not the .. biggest plagues our nation faces. And it's also not being addressed properly. Background checks need to be extensive. Applicants' social media activity needs to be reviewed/monitored. As you mentioned, waiting times need to be be appropriately long.
There is so much more that can be done if these weapons continue to be available to the general public.
But I will always maintain that eliminating them is the answer.