Just for fun, here are some quotes from Gygax's PHB about player character roles, with some of my thoughts interspersed.
First, a general introduction (PHB p 18):
The approach you wish to take to the game, how you believe you can most successfully meet the challenges wich it poses, and which role you desire to pay are dictated by character class (or mluti-class).
The cleric (PHB pp 18, 20):
Clerics principally function as supportive, although they have some offensive spell power and are able to use armour and weapons effectively. . . .
The cleric serves to fortify, protect and revitalise. The cleric also has a limited number of attack spells . . . In addition, the cleric has the ability to wear armor, carry effective weaponry, and engage in hand-to-hand (melee) combat with a reasonable chance of success.
This is very close to the 4e leader, especially the STR cleric or warlord.
The druid (PHB, pp 18, 20-21) is also described in terms that suggest a leader:
Druids . . . operate much as do other clerics, but they are less able in combat and more effective in wilderness situations. . . .
[T]he spells usable by druids are more attuned to nature and the outdoors then are the spells of other clerics or magic-users. Nonetheless, druids serve to strengthen, protect, and revitalize as the usual c;eric does.
I'm not sure this is an accurate description, though. The druid has noticeably more spells that target enemies, like Entangle at 1st level, Charm Person at 2nd level, Call Lightning at 3rd level, etc. The druid is something of a cross between a cleric and a MU. In 4e terms, it straddles the leader and (ranged) controller.
I think the AD&D druid is generally recognised as something of a challenging class to play effectively.
The fighter (PHB pp 18, 22):
Fighters generally seek to engage in hand-to-hand combat, for they have more hit points and better weaponry in genera than do other classes. . . .
The principal attribute of a fighter is strenth. . . . A good dexterity rating is also highly desirable. . . . Fighters are the strongest of characters in regard to sheer physical strength, and they are the best at hand-to-hand combat. . . .
Although fighters do not have magic spells to use, their armor and weapons can compensate.
There is no defender/(melee) striker distinction in AD&D - for reasons I've explained above. This calls out the fighter as a melee-oriented characer, though, whose resilience (armour and hit points) and weaponry are their main asset.
The magic-user and illusionist (PHB pp 18, 25-26):
Magic-users cannot expect to do well in hand-to-hand combat, but they have a great number of magic spells of offensive, defensive and informational nature. . . .
While they have might spells of offensive, defensive and informational nature, magic-users are very weak in combat. . . . [M]artial training is so foreign to magic-use as to make the two almost mutually exclusive. . . .
[W]hile magic-users are not strong in combat with weapons, they are possible the most fearsome of all character classes when high levels of ability are finally attained. Survival to that point can be a problem, however, as low-level magic-users are quite weak.
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Illusionists . . . are different primarily because of the kinds of spells they use. . . .
llusionists have different and highly effective spells to employ. . . . [T]hey are at least as powerful as normal magic-users and possibly slightly more potent at very high levels.
This makes it clear that MUs (and illusionists) are not weapon users, and certainly not melee combatants. Their power is their spells. But there is no very specific characterisation of what their spells are good for. The "offensive" spells are (in 4e terms) ranged striking ("artillery") and control ("anti-personnel", like Sleep at low levels and Cloudkill at higher levels). The "defensive" spells also include control (eg Web - though some might count this as "offensive") as well as abilities that in 4e become rituals (eg Wizard Lock). The "informational" spells in 4e are a function of Arcana skill (a mandatory skill for wizards) and rituals.
It is possible to see the AD&D wizard in its 4e version, but the ranged striking is notably weaker, at least in the PHB. (Later releases, especially post-Essentials, boosted it somewhat.)
Turning to thieves (PHB pp 18, 27):
Thieves use cunning, nimbleness, and stealth. . . .
The profession of thief is not dishonorable, albeit is neither honorable nor highly respected in some quarters. . . .
Thieves are principally meant to take by cunning and stealth.
I think the biggest change in class role between AD&D and 4e (and it continues into 5e) is with respect to the thief. The thief becomes a powerful skirmisher (melee striker in 4e) or sniper (ranged striker in 4e), and the focus on literal thieving (or dungeon-delving burglar) is dialled back.
Finally, monks (PHB pp 18, 30):
Monks are . . . disciples of bodily training and combat with bare hands. . . .
Monks . . . practice rigorous mental and physical training and discipline in order to become superior.
Monks have always been martial artists, and hence melee-oriented, but AD&D found it hard to pin down the way in which they contribute to this while differing from the fighter. 4e took advantage of some of its distinctive features (eg the role of movement in combat) to give monks a distinctive skirmishing role.
It seems to me that class and mechanical function have always been intended to be linked, but in AD&D some classes made this a bit tighter and clearer than others.