As for improved treatment of gunshots...
I researched this a lot for
Conflict, and my personal social circle has a lot of doctors, nurses, and paramedics. They say there have certainly been some improvements over the decades, but the biggest factor is time from injury to treatment.
Now, either the gunshot potentially kills you, or it just fucks you up for some years afterwards. For homicide rates and RPGs we're not really interested in the poor bastard who gets shot and survives but needs years of operations and rehab to be able to function even badly. So just consider deaths and treatment to avoid them.
In terms of the gunshot killing you, either it hits your brain or spinal cord, or it strikes a major blood vessel. There's not really anything anyone can do about a piece of your brain being pulped, it is what it is. It's the blood vessels where there was room for improvement.
For example, when someone loses a lot of blood, they go into shock and may die. Often they had to take time to blood type the person, and a transfusion wasn't always available - paramedics can't carry all the different blood types in their vehicle, rural hospitals won't have them all, etc. It turned out that a lot of the shock response was actually due to a drop in blood
pressure - so you could just give the casualty saline, that'd keep the overall blood volume up. You can't replace their entire blood volume with saline, they do need
some red blood cells carrying oxygen around. But the saline vs doing nothing would buy you some time to get them to hospital, or clamp the bleeding artery, and put in a proper transfusion. So that's one example of an improvement in techniques over the decades.
However, what they all say is that
time is the primary factor, by far. If you're losing a unit of blood every 5 minutes then you're in more trouble after 15 minutes than 5. The gunshot victims with the best survival rates don't get paramedics at all - their buddies on the scene bundle them up in the back of a car, speed off and then dump them at the front door of the local hospital - then speed off again. And that's because it's 5-15' quicker. An ambulance has to be called, driven to the scene, the paramedics get out and assess, and so on. But the buddies on scene don't have to drive there, they don't assess, they just take the casualty straight over.
(That's not telling you not to call ambulances when injured, by the way, there are all sorts of injuries where moving you around quickly isn't going to help.)
Likewise, gunshots have a 71-72% survival rate in the US, but had a ~90% survival rate in Afghanistan. The difference isn't body armour because the guy who had a round go
dink on his plate doesn't show up in military hospital as having a gunshot wound. The civilian-military difference is the guy getting basic first aid on scene, dumped in the back of a Hummer and driven back to base, or choppered off, etc. In other words: time.