Celebrim
Legend
If you gave them every single class feature for all the base classes in all the books... they would be extremely powerful, but they would be, by no means, invincible.
I didn't say that the standard was whether or not you are invincible, although obviously, true invincibility is functionally equivalent being good at everything. No, it is simply enough to violate the fundamental law of role playing to be good at everything, even if that doesn't imply absolute invincibility.
I believe that RPGs as we know them have several origins, but not the least of these are the sorts of games that children play back when they are innocent enough to enjoy play for its own sake. One of the things that ultimately disrupts these games is one or more children try to be good at everything so as to always be the center of attention. All adult RPGs are built around ways to prevent this from being a problem. It's one of the reasons that we focus so carefully on the idea of 'balance'. In essense, the adult RPG helps deal with player conflict and spot light grabbing by fairly distributing the spot light and by teaching the players to maturely accept the possiblity of losing. This is one of the features that allow people to keep role-playing as adults long after the innocence is damaged or gone.
Batman might have some seriously compelling storylines... but so does Superman.... and there's a guy who can do pretty much everything.
Superman is not (originally) a character in a RPG. As an RPG character he absolutely sucks.