I have to disagree with the "3 pillars equal" stance. As part of game design it is definitely a good way to go. But as a part of character mechanics supporting narrative it is a huge failure. If you look at fiction (and at real life, for that matter) there are people who are good at many things, and people who are really good at a few things. To allow the breadth of character customization that I (and many others I have played with) you must be allowed to focus in an area. Any attempts I've seen to allow everyone to "function equally in all pillars" have not allowed me to make a living and breathing character without having to twist his concept. Don't make everyone "equal" in all pillars, just "useful". Balancing both of these concerns for a variety of playstyles is exceedingly difficult.
I think that there are 3 main class archetypes: Warrior, Spellcaster, Skillmonkey. Within those there is a huge amount of distinction and hybridization possible.
To me an ideal fighter isn't necessarily identified by being the "best" at combat. His schtick is that combat is his thing. He knows it inside and out.
There is almost no possible combat situation where the fighter can't kick butt. In fact, he's so good that where a rogue or wizard may have one strategy to follow in a given situation, a fighter has his choice of two or three. The others might have to jump through hoops or burn daily resources when put in a tight spot. The fighter just defaults to plan b.
To me this would be the dividing line between rogue and fighter. Apply the same concept to exploration and/or interaction for a rogue. The fighter might have one way to get through a given noncombat "encounter". If that way doesn't work, he'll have to jump through a couple hoops and scramble, but won't immediately become useless. The rogue, though, simply defaults to plan b. He might even be good enough to counter the fighter's "tight spot moment", using his huge breadth of skills to remove the impediment the fighter doing his part in the "encounter". I think that another thread (the one about fleshing out exploration so it plays more in-depth and not so on off) is very related to this one. A better exploration pillar makes it easier to balance character concepts that don't want to be "the combat guy and the exploration guy and the social guy" all equally.