To answer the second point first, absolutely agreed that laws that go unenforced are useless. We do need to do a better job of enforcing the paltry laws we have now, in addition to whatever new ones happen.

However, that is stymied by current laws that restrict law enforcement's ability to do its job. For instance, ATF (The Bureau of Alcohol, Tobacco, and Firearms) is effectively banned from... using computers. No kidding:

The 1986 Firearm Owners’ Protection Act, passed with the backing of the National Rifle Association, outlaws the creation of a national gun registry. As a result, any documents the ATF scans must be stored as static images that cannot be searched digitally. I watched tracers sitting on the floor, thumbing through pages spread out on the carpet.

From: https://www.motherjones.com/politics/2016/09/atf-nra-battle-guns/

Even enforcing the background checks is actively undermined.

In the late ’90s, the ATF published reports that identified the guns most commonly recovered at crime scenes. Shooting victims, their families, and cities used this data to sue gun manufacturers and dealers. So the gun industry went to Congress. In 2003, Rep. Todd Tiahrt (R-Kan.) introduced a series of riders to federal spending bills. The Tiahrt Amendments, versions of which have passed every year since, prohibit the ATF from publicly releasing detailed gun trace data and limit its ability to share this data with other law enforcement agencies. “I wanted to make sure I was fulfilling the needs of my friends who are firearms dealers,” Tiahrt said. NRA officials, he added, “were helpful in making sure I had my bases covered.”

So yeah, let's enforce the laws we already have. That means getting the NRA out of the way and letting law enforcement actually use 20th century tools (to say nothing of 21st century tools) to do its job. But that won't happen until the NRA's stranglehold on Congress is eliminated.

To your first point, my limited googling just now hasn't found a solid resource tracking the rise in mass shootings. The best I've found is from Mother Jones, here:

https://www.motherjones.com/politics/2012/07/mass-shootings-map/

which only goes back to the early 80s but does show a clear upward trend. However, half of those recorded have happened since 2006. So there's a definite recent-change, not something from the 70s.

I will completely agree that the dismantling of the public mental health system was a terrible thing. We as a country completely ignore mental health and when we do pay attention it's just to use it as a scapegoat, especially so we can write off white-males as "just a mentally disturbed lone wolf, nothing to see here". (Of course, if a Muslim shoots someone then it's clearly because he's Muslim. But that double-standard is a topic unto itself.)

That said, blaming that for the rise in mass shootings is not, as far as I'm aware, supported by the data. Most people with a mental illness are not a threat to anyone; those that are, are primarily a threat to themselves. Gun suicide I can totally see linked to mental health issues, and we absolutely need to take more steps there (both on the gun side and the mental health side). In short, citation needed.