Permeton, when looking for a passage to define the 'roles' described in previous editions, as pertaining to those used in 4E, it may be useful to check whether any of the passages quoted actually uses the term 'roles' along with those of 'Defender', 'Striker' or whathaveyou.
These passages you have chosen merely describe the Classes in question and simply describe what they are good at - rather than there predesignated jobs in a playing party.
What do you think the difference is between
describing what a class is good at and
describing a class's predesignated job? I don't see any difference. The reason a fighter's "predesignated job" in 4e is to be a defender is precisely because
that's what a fighter is good at. Nothing in 4e stops you trying to play your fighter as a leader, just as nothing in AD&D stops you trying to play your fighter as a support character who fortifies, protects and revitalises much as a cleric does. It's just that, in both systems, you'll find that your fighter is pretty weak at this function compared to a cleric. (And also in AD&D, if the GM is using the training rules, but not in 4e, you'll find it is harder to gain levels because you're playing your fighter in a spirit contrary to its "predesignated" function.)
In AD&D you can try to correct this deficiency in your fighter by multi-classing or changing class into cleric. In 4e, it can be done by (eg) multi-classing into a cleric and then taking a cleric paragon path (this is what the fighter in my 4e game has done, for instance).
As to whether the roles are exactly the same - of course they're not, 4e and AD&D are mechanically different systems. This was hashed out in a long thread 6 months to a year ago. The basic difference is that, in 4e, because melee is by default non-sticky there is scope for a difference between the striker and the defender roles (strikers exploit non-stickiness to impose damage while avoiding it, defender's generate stickiness and soak damage as well as inflict it) whereas in AD&D melee is sticky by default and so the interesting melee characters need to be able to both soak and inflict damage. The lack of in-melee movement in AD&D also means that there is not as much scope for forced movement as a debuff, nor for giving allies free movement as a booster - and so the "controller" and "leader" roles (using 4e terminology) are in some respects more narrow in their mechanical suites of options.
In Unearthed Arcana there is an attempt to create a class that might play a little bit more like a 4e striker - the Thief-Acrobat with its Evasion ability - but I personally don't think it was a great success, as the mechanic is clunky and the T-A's ability to actually strike is pretty limited. So Evasion basically ends up playing like a clunky variant on the monk's ability to avoid damage on a successful save - and the monk version is what ended up being implemented across both rogue and monk classes in 3E.
But in any event, 5e is in all these respects closer to 4e than to AD&D - melee is, by default, non-sticky and in-melee movement is part of the combat resolution system, and so forced movement and granted movement make sense.
4e was pretty flexible in the way that it grouped various suites of abilities - eg paladins heal, buff and "defend"; fighters strike and "defend"; invokers both inflict forced movement and grant movement to their allies; etc - and there is no reason why 5e can't be at least as flexible.
All of which is to say, there is nothing about 5e and its approach to roles that makes the warlord - a non-magical character whose schtick is granting movement to allies, restoring their hp, and otherwise buffing them - particularly inapposite or out-of-place.
EDIT:
Here is the thread from January this year. I haven't reviewed the whole thing, but some of the interesting action seems to be taking place in posts in the 600s.
