Functions were always there. But that's not the same thing as explicit roles.
A Fighter was a fighter. He could serve as a defender, he could serve as a striker. In 3e he could even serve as a controller. Spec how you please. He also had the classic "Fighter's lockpick."
4e? Defender. With carefully defined power ranges to avoid him stepping on the Rogue or Wizards toes.
The 4e fighter is a lot
better at stepping on the wizard's toes than the 3e fighter is. As for the rogue's toes, it's much
easier to create a 4e fighter with skillmonkey tendencies than it is a 3e fighter/skillmonkey due to the terrible skill points the 3e one gets. 2+int mod skill points/level out of about 36 skills with no easy way to get more doesn't go half as far as 3 skills out of seventeen, all skills levelling automatically, and feats and multiclass feats gaining you an entire extra skill. Fighters are also near-strikers as it is - and with two multiclass feats they can gain sneak attack 1/fight and the ability 1/encounter to hide in places only a specialist rogue can.
You are simply wrong in your claim.
Explicit roles limit PC options, player creativity and game design options.
Except that as I have shown it's easier
to step on the toes of the rogue with a 4e fighter than a 3e one. I can easily make a 4e human skillmonkey fighter who at first level
wears light armour (hide), carries a rapier and shortsword, and has the skills Stealth, Thievery, Perception, Streetwise, Intimidate, and Athletics trained. Oh, and sneak attack 1/fight. (I can do something similar by 4th level with any race).
Translating those skills into 3e you'd need Hide, Move Silently, Open Locks, Sleight of Hand, Disable Device, Spot, Listen, Search, Gather Information, Knowledge (Local), Intimidate, Climb, Jump, and Swim all trained at effectively maximum ranks. Find me the fighter who can do that
in 3.X. Hell, it's pushing towards the limits of what a dedicated rogue can do in 3.X
Explicit roles lower the theoretical
limits of PC options (so do explicit classes). But a class as crippled as the 3.X fighter with its 2+int skill points/level is nowhere near those theoretical limits.
Lets suppose for example you want to make a character who (to borrow an MMO term) does debuffs.
In 3e you might make a Duskblade, or a Binder or talk your GM into allowing Bard who applies his bard buffs as malus to the badguys instead of bonus to the good guys. Or pick a spell caster and gun for debillitating spells. Necromancer would work well.
In 4e? You are outside the accepted design space. Possibly you could shoehorn that into the controller role. Maybe they even did that later on, I don't know.
This, again, is simply not true. If you want to straight debuff single targets, the feylock springs to mind - and the wizard does a fine job too. Surprisingly so does a well built charisma-paladin. For area debuffs the wizard works extremely well. A bard built for debuffing also works well.
Look at 7th sea. Dungeon crawls were solidly supported by the worlds design. The 4 roles of D&D? Almost completely absent. (I say almost because you could go for an arnoured fighter and try to tank. Still no healers to back you up though.)
And 7th sea is a different game from Dungeons and Dragons
Frex, one of my favorite late 3e classes was the Dragon Shaman. With hindsight it shows clear signs of being an early dabbleing with 4e design philosophies. He's got some heal, some buffing, minor area damge. A leader/controller then.
Sounds like a 4e cleric. Or a 4e bard built with area attacks.
You know what I did with them? 1 level as a Knight or Fighter to get heavy armour and martial weapons and turn them into frontline Defender types.
Easy in 3e with no explict roles, but the same functions. In 4e? Not doable, because of the rigidity of the design specifications.
In 4e as I have mentioned the Cleric is a leader with a minor in control. Use the class options to swap healer's lore for battle cleric's lore and we have our cleric in heavy armour. Then we take either the multiclass paladin or multiclass cavalier feat and we get either a mark or a defender aura. Weapon attack powers - the cleric gets them. And now we have our front line leader/controller who is able to defend.
So much for your claim of "Not doable". Once more your claims about 4e are simply not true
Our experiences with the two sysyems are very different then