AbdulAlhazred
Legend
As I said before, the roles were DESCRIPTIVE; they described how the character was USUALLY played. Now, it was certainly possible to break the molds (something every edition but 4e did right; allow out of the box thinking) but the fact that they could be broken does not deny that a lot of people DID view the guy with low AC and high HP as the one to get beat up in combat or that the moment you find yourself with half the party in single digit hp or dying, the "gee, maybe someone should have played a character with cure light wounds" didn't happen.
4e got it wrong when it said roles were PRESCRIPTIVE: they defined the class more than described it. Why does a fighter tank? Because he's a defender and that's what defenders do. Why does an artificer heal? Because he's a leader and that's what leaders do. That kind of thinking got 4e in trouble with grid-fillers, boxed thinking ("This is a new leader class. It MUST have encounter-based healing.") and rewriting of flavor to make the old classes conform to the new paradigm (such as druids losing most of their healing magic until Essentials). That was a bad choice, and one that Essentials started running away from pretty hardcore (though as early as PHB2 it was noticeable that classes were often descibed as X, with a little Y)
But to assume that the concept of roles sprung forth whole cloth in 2008 is ridiculous. It was an attempt to give game-mechanics and codify something people had been using unofficially for decades. 4e just went overboard with its implementation.
Well, I agree with the last part, but I think that the first statement you made is just incorrect. 4e can be quite flexible. You're not going to make an archer ranged striker using the fighter class, but a fighter can range anywhere from the GWF builds, which focus on high damage output and are basically strikers, to a 'sword-n-board' DEX fighter that is maximal defender and actually takes hits for his allies, to a super sticky Pole Arm Momentum fighter that is effectively a short-range controller (no enemy can disengage from him, not even with teleport). All of them will have CS/CA and the toughness needed to 'defend' to some degree, but they can quite effectively fill other roles. If you MC or use other options effectively you can achieve even more flexibility.
I don't think there's anything wrong with what you call 'PROSCRIPTIVE' roles. The problem was that pre-4e D&D's classes were very hit-or-miss haphazard designs. A designer wouldn't really have any clarity as to what the class' niche was and what it needed to achieve to work. Just looking at 1e, you had problems with the thief (too weak in combat, just got one backstab per fight and a weak ranged attack), the monk was worthless because it really didn't have a role at all, ranger was cool, but also lacked a real unique shtick in combat, and the wizard was all over everything as a be-all end-all swiss army knife. By 3e where you had lots of complex options per class it was a pure train wreck. Half the classes were really UTTERLY worthless, and the other half could do ANYTHING.
4e was a necessary correction. Sure, some classes were shorn of unneeded parts, and others got access to abilities that were necessary for them to be able to function adequately. The proof of its utility and success is in the pudding. All the 4e classes are VERY solid. Each does its job, does it reasonably well, and its easy to know what job was in mind for it. Yet you can still bend a class to fit at least some other concepts, and beyond that use a different class and bend THAT (IE ranger being your 'bow fighter' option).