Slinslin, you can't figure out what you're arguing. Obviously the biggest talents are going to try to come out more quickly. These days, if someone stays in school for three or four years, it's only because he doesn't think he's ready to be a high lottery pick before then. So yes, of course, the straight-from-high-school crowd is going to be a better crop than the whole population.
The question is whether a year or two in college would have helped those high school rookies. There's no way to know that, because we can't compare the actual LeBron James with a LeBron James who went to college for a while first. For that matter, we also can't compare the actual Kevin Durant with a Kevin Durant who came straight from high school, because the rule was different for him. Both players entered the league as quickly as they could, and if the rule had required each of them to stay in college for three years, then each of them would have stayed in college for three years.
Circumstantial evidence suggests that coming straight from high school doesn't do players any favors except in the pocketbook. As we've already discussed, only two (Stoudemire and James) won Rookie of the Year. Bryant, McGrady, Howard, and the others who became All-Stars needed some seasoning first: they entered the league behind the curve.
Both Stoudemire and James have had their own issues which could well be related to turning pro too soon, although it's impossible to say for sure. Stoudemire has been hurt a lot. The eye thing was a fluke, but maybe some time in college would have taught him how to take better care of his knees and back. He almost certainly would have gotten some training in defense and boxing out, which he still lacks, and which will probably prevent him from reaching his potential as a player. As for James -- who is now 26, by the way, and has been in the league for eight seasons, so no longer exactly a youngster -- his continued immaturity is obvious, he has shown almost no leadership in the playoffs, and he still hasn't figured out that NBA games are about more than how good he can make himself look. Would some time in college have helped him? It seems like a distinct possibility.
The only two high-school players who have gone on to become stars on championship teams are Bryant and Garnett. Bryant is the son of an NBA player and grew up in Europe, so he is a special case in every possible sense. Garnett was like James for most of his career, failing to show real leadership in the playoffs and wearing out his welcome with each new teammate within a couple of years. Finally he lucked into the situation in Boston, but does one title as a second fiddle really count him as a success story for the high-school group?
It simply isn't possible to argue that coming to the league straight from high school was better for the players who did it. Sure, they may have dodged a career-ending injury, but that scenario is not enough by itself to justify the policy. Other than that, as a group, their careers have been plagued by underachievement, immaturity, selfishness, and -- except for Bryant, who really is in a class by himself -- a grand total of one championship ring.