And I suppose that depends on how nitpicky each person is about the things that make up each "role" and how much do you need of it for it to be considered "new" or "always there". If they're saying the four roles as catagorized as 'defender', 'striker', 'leader', and 'controller' didn't exist before 4E, then sure they're right. 4E invented those terms. If they even say that the role of say the defender didn't exist before 4E because the game mechanics invented for the 'defender' role (marking and the like) never existed before 4E (and thus ipso facto the 'defender' didn't exist), then sure, again those people could say they were right.
But at the same time, if someone sees 'defender' and equates that merely with "heavily armored guy that tries to interpose himself between the enemies and the squishies" or more colloquially "the tank"... then those that say that the concept of defender has always existed would also be right (because that was certainly a facet of the fighter that's been played up since the beginning, and is the entire reason why the concept of "the tank" came into existence in the first place.) By the same token, if someone sees 'leader' and equates that to the guy that helps keep the rest of their party buffed and on their feet... that's also an idea that's been in the game since the beginning and has been used by many tables since the start of the game. We didn't call that character a 'leader' obviously, we called it 'the cleric'. But what 'the cleric' did in the game for a lot of tables has never been in dispute.
So it really all comes down to how closely are you parsing the terms themselves that are determining whether you think the roles have existed in the game before 4E. If you are only looking at the conceptual idea of what the roles tried to accomplish, then yeah, you'd think those concept have always been in the game. But if you are looking more in the micro and the rules, mechanics, and definitions that were given to the 4E classes to be and do those roles, then you also are right in that they didn't realize exist in of themselves until 4E codified them.
So there's really no point in arguing it, because we're not all going to agree with the starting point of the conversation.