So, you're basing your assessment on what some military folks and you think, based on news coverage and social media videos. You seem to have more limited social interaction with cops; not really surprising, a lot of cops kind of keep to themselves off the clock, for lots of reasons.
Let me start with a story... I was assigned to a regional task force for several years. One of the advantages and cool parts of that was the opportunity to go to some cool training. One of those courses was hosted at a military base, and one of the the things we did there was some simulator training. I don't recall all the scenarios, but two stuck in my mind, because every cop responded to them the same way -- and "failed" by the military standards. The first was a checkpoint, where we were slow to shoot per Army expectations. But -- we weren't guided by the rules of engagement in some sandy overseas locale; we were guided by the laws and court decisions interpreting the 4th amendment and the use of force. (Yep, use of force is a seizure; most of it's covered under the 4th amendment.) Under those rules, we didn't have grounds to shoot until a later point than the Army would have. The other was a suicidal soldier, who had a pistol on a table. Every cop shot the guy much faster than soldiers would... Why? Because, as soon as we are presented an imminent threat of deadly force, we can respond -- under those same rules I mentioned earlier. My point -- military assessment of police use of force isn't always going to be accurate. (And it goes the other way -- cops shouldn't spend a lot of time tearing down how a military unit did something, either.)
You've watched documentaries... how many of them had an agenda? Most that I've seen were clearly intended to support particular points of view -- often anti-law enforcement. Honestly, I haven't seen a lot of true documentaries -- mostly interest pieces on a particular class in an academy, a few tv shows (COPS is not particularly accurate; to a half hour of interesting tv, they usually follow 6 to 8 - or more - officers for an entire shift...), and so on. And how interesting is it to watch a verbal de-escalation, for most people?
I'm going to recommend one book,
Force Decisions by Rory Milller, because Rory wrote it particularly to address a lot of these sorts of issues. (And a very insightful person wrote a very short opening piece to one of the chapters...
) and I'm also going to strongly encourage you to look into attending a
Citizens Police Academy. The purpose of these programs isn't to make you a cop -- but to give the public a chance to see what police training and police work is really like, rather than what is portrayed in TV and movies. There are also programs like the one shown in this news clip:
which give you a taste of what it's like to walk up to a car as a cop...
As to the number of people killed... No cop that I've ever met goes to work wanting to kill someone. And if they do... I want them gone, yesterday. That said -- we also all have families, friends, and loved ones -- and we will go home to them. Our job is to go towards the guns, not away. In the US -- we strictly limit what the military can do on our shores. (Look up
posse comitatus.) It's not the same way in other countries, so some of the situations we send cops into are handled by the military in other countries. That's one way the numbers change. Another is that we have a much, many times much, more diverse population than many other countries -- which is often much more likely to react less compliantly to the police. And we have a whole lot more guns (which I don't have a problem with; I strongly support the 2nd amendment) out there... Unfortunately, lots of them are in the wrong hands (which I do have a problem with...). So that's another factor in the numbers... and another reason it's hard to compare some things about policing across different borders.
Oh, and as to hiring smart people... Every agency I know certainly wants to hire smart people. The job of a cop today demands a whole lot of intelligence, coupled with life experience and judgement, and plenty of street smarts and common sense. You can't read and apply the regulations, the laws, the court decisions, and everything else if you're dumb. It's kind of like suggesting that an infantryman or Marine is too dumb to do something else...