Have you ever leveled your character too fast in an MMOG? I remember some game I played that allowed the player to turn off their experience gain if they wished. They did this because (1) some players fell behind their friends because they couldn't spend as much time online, and (2) because leveling too fast trivialized vast amounts of content for players that didn't want to invest time in multiple characters; they wanted to do every level 1 quest there was in the world without it being trivialized or unavailable to them because they had outleveled the content.
Isn't that a scream? Players complaining about leveling too fast and not being able to fully enjoy (in a meaningful way with their primary character) the full breadth and depth of what the developers had put in the entire game. Players that took their time and explored every nook and cranny of the game, the lore, the quests, etc. Yes, there are players like this; for instance,I found out in one game that I couldn't even max out all my weapons skills (raising my ranged, blunt, blade, unarmed, etc.) to max for a level without going up yet another level or two .. meaning, I had no means by which to simply raise one set of skills without raising my entire level and increasing the upper limit on all my skills. At the same time I was becoming too high a level for my current recipes; they were for level 6, but I was now level 8 ... just because I wanted to increase my unarmed combat to its max for my level.
And there, my friend, is the organizational nightmare that is the level-based system, and why it is so easy for current games to be broken, horribly unbalanced, and unplayable for many.
How do you fine-tune and balance such a chaotic system? You can't please almost anyone when it comes to how fast one finds themselves leveling when they are simply moving along the programmed developmental pathway for their "class" or "role". Also, you have to beware how many options you allow the player to have or else they'll get stuck and be largely unable to progress if they make lousy developmental choices along the way; best to confine their options to a very narrowly-defined and tested set so that, if they really work at mucking up their character, it will still be viable and they'll still be progressing down the level path (even if most players will avoid grouping with them). If you're not min-maxed, you're SOL.
Of course this system makes for what most call a "dumbed down" game; you have to dumb a game down if you want to avoid structural problems with the advancement path. The fact is that in a level system all characters must be in roles, they must be on paths, they must play a class, or else the door is open to chaos and failure down the road, because challenges must be designed to fit certain stages of a character's development and how their role is defined and powered in relationship to those challenges. Only, the problem is that everyone plays differently and has different expectations and, even after the best testing, unforseen advantages and disadvantages will be found out.This is why a good section of every game population considers the game broken regardless of how it is balanced, nerfed, adjusted, or fine-tuned.
In other words, a level & class based game necessitates a very controlled and narrow development path for every player. End-Game scenarios require fine tuning of group potentials so that the end game content can be challenging to a certain number of players in a group or raid. The chaotic nature of the scope of even these dumbed-down games ensures that everyone is going to consider some aspect of the game broken.
In a sandbox game, the "end content" is whatever the player wants it to be, and it provides a plethora of development avenues and options. If I wish to raise all my combat skills to say, level 3, then I can do so, and I'm just a player with all my base combat skills at level 3. That doesn't make me a level 3 character; it doesn't trivialize any other content. It might make me more diverse when it comes to combat, but it doesn't remove me from being able to get those magical knitted gloves offered by one of the first quest givers in the game. Can I get over-powered for certain content? You bet; that's the way it should be. There are occasions when I should be monstrously powerful, even compared to other players who have been in the game as long as me; just as they may be able to produce crafted items I have no means to create, and just as someone else is selling super-buffs in the marketplace or at the city gates, even if they have no combat or crafting skills.
Yes, that kind of game doesn't avoid chaos; it deliberately embraces it. The only way to offer players true character freedom and customization is to just let them develop their avatars in whatever direction they wish. If after a week they are incapable of defeating a foe others can with ease, well they can simply start studying or training skills that will allow them to win that battle. Nothing they will have done up until then will be wasted; they'll still have all those other skills they invested their progression time into.
You see, you can't break a game that doesn't try to generate control patterns enroute to specific end-game content. If it takes 10 players to beat X in one case, and only one to beat it in another case, so what? It all depends on how you, or you and your guild have organized the development of your characters. There is no "balance" whatsoever because there is no objective, linear goal to balance anything for.
You can't break a game like that. If, during PvP, you always end up dying just a whisper before your opponents, then it's time to train up some endurance or stamina and increase those hit points, or speed up your attack, or make your attacks more potent, or get some healing skills - whatever fits the need of your character and suits the style of your play.
A game like that becomes all about the strategy in relationship to what you want to accomplish in the game and has nothing whatsoever to do with how much time you have to invest in sitting at your keyboard punching the same buttons over and over.