The reality of all of this is nothing changes overnight; controlling domestic terrorism such as this isn't a one-step or two-step solution, but like an engine, requires multiple parts to work together over a prolonged period of time to make an impact. It's not impossible to do, but requires commitment from all parties to make it happen.
Mental health issue? Sure, we can strengthen this, but would have that alone prevented this? Would these individuals even have been flagged?
Background checks? Of course these need to be better than today's backdoors, but how do you regulate the secondary market of consumer to consumer?
Limiting high capacity mags? Makes sense, but only a handful of states have laws against these and it's easy enough to acquire one from another state.
Assault weapons ban? Mass shootings are undeniably up since the ban ran out, but even if we disallow the manufacture of new ones, the amount of existing ones is prevalent.
Gun buybacks? I know many who would sell there's for a nice markup in return and even though that would cut the existing population, many would choose to hold on to them anyway. There's also the outstanding issue of how you pay for it.
Withstanding from all of this is not giving a platform to this radicalization from politicians, special interests and tech companies who house more data about you than you could possibly realize and could better flag problematic behavior.
In short, change is possible, but big ideas will require big solutions. You can't piecemeal such a thing out and expect changes. But it's entirely plausible to reduce the trend of mass shootings down over time through a sustained and coordinated effort with multiple workstreams in unison.
Otherwise, just a matter of time before the next mass shooting and we regurgitate this whole conversation again and wonder what we could have done.