You are assuming. Something that should never be done in debate format. We never once see Vegeta at a point in time unable to use his powers. Even during flashbacks, though as far as we go it appears to be about gohans 4 year old range. You assume he was trained, but it is never once stated he was only able to use his ki because of training. I am guilty of the same thing on the reverse side of that coin. The only alien we ever see that needed training was Goku, though it could feasibly be argued that, during Dragonball either A. The bump to the head totally screwed him up, (which is true) Thus his need for the training that any other human on the planet could have gone through or B. Despite knowing he landed in a spacecraft, the saiyan race was not yet thought of, thus it is a retcon (a poorly thought out one at that, much like the medi's which we'll get to) and is quite simply a silly point for either person on either side of the debate to try to use.
The only two characters I can think of that display mastery over ki as children are Gohan and Broly, both of whom did so under extreme duress. Even then, Piccolo had to train Gohan to be able to a) learn to control that power and b) become proficient at combat. Being able to simply "use" ki isn't enough to make you a serious threat. It's the potential for violence coupled with power within an individual combined with the knowledge required to employ that power that makes one dangerous.
Secondly, Gohan Senior clearly had to train Goku to fight for one, and he later had to learn to use the kamehameha, through osmosis. He did it with ease. Why? Because he had potential. But potential without the means to employ said power is nothing. Had Goku not seen the technique, he never would have performed it. How do we know this? That became his main attack for basically all of DB and into DBZ until he began to train under others. If you don't know a thing is possible, or if it never occurs to you, you'll never think to perform, regardless of how easy it may come to you. It all comes down to training and practice, a lesson learned time and again in the series. Nothing worth having comes without hard work.
The Jedi Order was in the market of creating defenders of peace, much like a police. Not warriors like an army. Two extreamly different ideals. See, the good thing about arguing this, is that for the most part, minus some after ep. 6 comics, all of the Star Wars stuff exists in the same canon universe. You can argue that the Jedi Order from the prequels were how you described, however the order from the time of say KOTOR (which is also canon) was not, nor was the Order after Luke took over. The commonly known Order was the way they were because, even though they preached about no emotion, they were fearful that the Sith would rise again and it was that fear that gave birth to their most dangerous enemy.
That's a matter of opinion. The Jedi were essentially brainwashing children into thinking their way, and then employing them as enforcers throughout the galaxy when they were old enough. They were religious zealots who refused to stray from their dogma, ultimately leading to them almost becoming extinct as an Order. They taught the children to be wooden, to deny their feelings, and as such pushed the more independent members of their ranks to the Sith, if only out of sheer curiosity, if not complete outrage at being told what they feel is wrong. To deny what we are is a recipe for disaster. And in the end, their greatest champions were those who neither succumbed to the Sith nor the Jedi, but chose instead the Grey path.
The point here with the Star Wars thing was something totally different from DB, and I mearly used it to show the relation of how ki was viewed.. why it became it's own debate is beyond me. Also, for the record, I never once said people that hone their craft wouldn't be better.. I said everyone in both universes (DB and SW, in DB a little different as humans only had a set potential they could really reach) had the ability to use ki/Force and that the Force wasn't subject to having some retcon disease running through your blood stream in order to become more powerful. Just like ki, it depended on the person, their own bodies potential and will.
And I'm stating the children of force adepts/masters of ki will be more powerful than those who weren't so lucky to be born to powerful parents. What's my point? The Saiyans were an old race, who had been cultivating their ki and breeding for quite some time. Most other alien races are fairly old, as displayed by their technological prowess. Humans, however, are neither as advanced nor as powerful as the other races. Why? Because its young. Given time, there is nothing that states humans could not become the most powerful race in the Universe.
I'm going to skip your second bit of bold and just move to the thrid, as addressing it in turn addresses the second bit anyway.
He gives them ample opportunity to stop what they are doing, and in the end is forced to kill them. As they leave no other option. Why doesnt Superman kill Doomsday? Because quite frankly he can't. He beats him back sure enough every time, but every time it is by the skin of his teeth, People like Luthor you can throw in a prision or send them back to their own dimension. Back to DB here, people like Cell who can blow up a planet by blinking their eyes makes it extreamly difficult to allow them to live, and protect the planet he swore to protect at the same time. Every single one he has killed has been in the intrest of protecting his friends sure.. but he clearly states a multitude of times that it is also to protect the earth and all the people living on it. Hell, that's practically how Dragonball ends, with him promising Kami that he would do everything in his power to protect the planet. At the end of the series, that even gets extended to him taking it upon himself to defend the entire universe from Buu. He, like Superman fights for those who can't for themselves. The only real difference is that Goku and co. Tend to only focus on the bigger problems.. so if anything I guess they are lazy.
Why doesn't Superman kill Darkseid when given the chance? It isn't in him to do so. Everyone, and I mean absolutely everyone, has the potential to do good and turn over a new leaf. Superman believes that with every fiber of his being. That is what makes him such a shining beacon of hope. He doesn't give in to pragmatism. Darkseid will undoubtedly come back and kill a shitload of people, and knowing this, he is allowed to carry on. Superman is simply incorruptible.
But more importantly, Superman's first instinct is to reason with a person, empathize with them and then try to talk them down. He doesn't want to fight. He doesn't enjoy fighting. He doesn't enjoy conflict. It brings grief to his heart to have to fight. Goku, on the other hand, will fight you at the drop of a hat, enjoys fighting and conflict and actively seeks it on his free time. He defines himself by his battles. He is a warmonger.
I'm confused on this next be.. showing mercy and knowing you can subjugate every person on the planet but choose to act as it's savior instead are two different things. Right, and Goku and Superman both show mercy, and act as it's savior.. what's the point being made here?
The point is Goku is purely reactionary. If it weren't for the fact that his very presence is what attracts every single villain in the Universe, he'd be content to sit on his ass all day. He wasn't out there stopping crimes, creation diplomatic relations with various nations in an attempt to forge a lasting peace, creating new technologies and overall paying attention to the welfare of the average person. He stops the "big" problems, sure, but there's still a poor man-dog living in the alley with 2 bucks to his name after getting wounded in one of the military excursions with Cell.
No, I'm not confused how they work. However they are canon parts to the characters history. That's what I was addressing. Example 200 years from now, someone finds the dragonball manga and they read it.. that's it, it's the history of all the characters. Same person, finds every Sups comic ever printed in some nerds basment.. that's the total history of those characters. It's not like nazi Sups was written by that kid in his basement, but is official to the echaracter's overall history.
No, they aren't simply one character. They are each their own separate entity. The Red Son is not our Superman. Superman Prime is not our Superman. It's similar to Marvel where there are essentially infinite Earth's, each with their own X-Men, Avengers, etc. But they aren't the same people. Not by a long shot. Then you have one-off comics and "what-if" comics. Each Earth, each Universe is given its own designation.