Do you read history? I read quite a bit. I have spent a great deal of time reading about knights and medieval warriors.
They trained from a young age to fight. They didn't see battle for a long time, but because they had sparred, trained with many different weapons, trained to fight on horseback, and learned various tactics and strategies for fighting they were very prepared when they stepped on a real battlefield. So they might live long enough to gain the practical experience of the battlefield.
These men were not the type of men to die easily even to a more skilled warrior. Their training very much prepared them for the battlefield. It was nothing like modern day school.
I view the training a wizard or fighter have as I do the training of those medieval knights. They have spent much of their life training in weapons and armor, sparring, and practicing combat maneuvers. When they start adventuring, they are special operations soldiers just out of bootcamp. A higher class of indvidual than your standard guard. And they have been rigrously trained so they will not die in the first battle they enter to a single hit.
No one sends a boy on the battlefield if he isn't trained to do the job expected of him. I guarantee you that a 12 year old boy trained to be a knight and that was a knight's squire would beat a 20 year old modern man of today in a fight. He would match up in hand to hand against fairly advanced modern hand to hand warriors due to the amount of training he would have received in arms by the age of 12.
So this is a matter of how we view an adventurer's young life. To me a person starting out on an adventure is the apprentice of a stronger wizard or fighter who would not think of letting a student go on their first adventure unless they were fairly certain they would be able to survive.
I think 4E does a better job of simulating the amount of training that a young adventurer would have.
Truth be told, I think this is somewhat of a problem that people have with 4e. Lots of folks liked the rags to riches story of some farm boy going out to make a name for himself and doing just that. Unfortunately, that's one of the points of "Well, sorry, but your play style no longer works."
I think the diehard 3E guys who haven't spent much time studying 4E or don't know the ruleset very well want to argue. So they make false statements based on shallow experiences with the 4E system that don't tell the truth about it. It's their way of promoting anti-4E propaganda rather than just saying the simple truth: "They didn't give 4E much of a try, they like 3E better, and they don't want to play 4E."
If they said that, then I would have nothing to say. That is an opinion.
Stating that the 4E classes feel homogenous and can't be made as distinctive as a 3E class is just an outright falsehood born of either unfamiliarity the 4E PHB classes or an outright attempt to propagandize against 4E. Either way, I aim to dispel that myth.
I played 3E a long time as both DM and player. I owned every splatbook, the PHB 2, and some 3rd party source materials that further expanded options for characters. I know the 3E system better than most that play it, and the few that know it better than me...well, good for them.
I've played 4E now. Right from the beginning I had more options than I ever had with the 3E PHB. I have never had such trouble making a choice of characters as I have had choosing what race and class to play in 4E.
Not only did they make each class and race unique and individual. They also made each one so good that it is difficult to choose which one to play. I never had that trouble in 3E. The best races were obvious for a particular class, the best feat builds were obvious for a particular class. That isn't the case with 4E. That to me means they did a great job differentiating each race and class as well as balancing them so that one didn't stand too far above the other.
I like that I have a hard choice choosing whether to elf, dwarf, or eladrin. I like that I have a hard choice choosing whether to be a char or str based paladin. Each one plays unique and can give you a very useful benefit. It makes you fret to pick one path or the other because of what you'll lose by doing so. If that isn't differentiation with strong touch of balance, I don't know what is.
I don't think you got the issue of the "classes feel same-y." It's not based on classes not having different "builds" as much as it's based on the Powers system. Classes feel same-y because, quite literally, they're supposed to. Wizards made it one of their big goals in 4e to homogenize mechanics to ensure the classes remained balanced. Classes working the same is, in all honesty, one of the things 4e uses as a selling point. Denying this isn't just saying "you're wrong" to the players, it's saying that Wizards doesn't know their own game.
People say classes are same-y because they're comparing it to 3e where several classes all used different mechanics entire. Even straight from the core books there was a difference between how class mechanics worked with different classes or builds, that was big in some cases (wizards and non-casters) or a smaller difference (sorcerers and wizards). But the thing was, the difference was still there. In 4e, because of the Powers system, fighters fight like wizards fight like rogues fight like paladins fight like every single unreleased class will fight. I'm not saying that's inherently a bad thing - again, this is one of 4e's selling points. It's just something that some people will like, and others won't.