You may or may not accept what I'm about to tell you, and if you don't accept it, I've done this enough that I know nothing I say would convince you.
Some of us who are adamant about Oswald, and Oswald alone, being the President's assassin did not always believe that way. We are not "true believers" in the sense that no evidence would convince us. I am a "true believer" because I started out as a skeptic, and became a true believer because of the weight of the evidence. Ineed, before I looked beyond the conspiracy books, I was more than a skeptic of the Warren Commission. I had seen a lot of information on 1970's television, and read some books, and knew that the Select Committee on Assassinations had found that there probably was a conspiracy. Based on that information, I assumed that there was a conspiracy. Determined to learn more about this conspiracy, I began research, and instead found that there was no conspiracy at all.
It's incredible the amount of misinformation that authors put out, and you have repeated some of it here. For example, the Mannlicher Carcano rifle is not some piece of junk. It's a perfectly good World War II era military rifle. I once saw a 1942 magazine article talking about what our servicemen would face when they went into battle. I remember that article saying that "Giuseppe's rifle" had an accurate range to 800 yards. Oswald's longest shot on November 22, 1963, was 88 yards.
I'm not a great shot with a bow and arrow, but I know people who could repeat Oswald's accuracy and timing with a bow. (I'm cheating just a tiny bit on that one. The usual amount of time allowed for the three shots is 4.3 seconds, but subsequent research has shown that the three shots probably actually took more than 8 seconds to fire, which would put it within the range of timing and accuracy of a very good bowhunter.) For a rifleman with a bolt action rifle, 4.3 seconds is more than enough time, but a somewhat difficult shot. With 8 seconds, any second rate marksman could have done the job, and one of them did.
At any rate, I know far more about the Kennedy assassination than any sane person ought to know, precisely because I was a skeptic. However, reading the evidence changed my mind. The evidence against Oswald really is overwhelming, and there is no evidence that there was any involvement by anyone other than Oswald. The books, movies, and probably web pages that claim otherwise are presenting very distorted views of reality that make it look like evidence exists, but if you examine it skeptically, you'll see that most of that evidence is distorted, except where it is just plain manufactured. If you have a few questions, and are genuinely skeptical, I can see if I could answer them.
You have an advantage that I didn't have. I was researching this stuff more than 20 years ago, before there was a world wide web. I'm sure the truth is a lot more accessible than it was then. On the other hand, the availability of the internet has made misinformation much more accessible as well, so it might be more difficult to sort truth from fiction.