OK. I'll try this one more time. Long post to follow. Where I make statements about play-styles, these are in my experience in the various groups I have played in over the last 35+ years. They may not be your play-styles, but they ARE ours.
Let's start with the basics. D&D, as a game, uses dice mechanics to adjudicate the results of player actions. The mechanics of these rolls have changed between various incarnations/editions of the game. The first edition and AD&D, because they were adaptations of what originally was a tactical war-game, had a variety of (generally) disconnected mechanisms for adjudicating how a dice roll affected what you, as the character, were trying to accomplish. Sometimes you rolled high for success. Sometimes low meant success. Often you would roll different types of dice (d20 vs d100). Because of these differences, there was very little synergy between the various mechanisms. The only way to increase your sneak skill was gaining a level in thief or through using one of a handful of magic items (Dex had so little effect that the maximum bonus on most thief skills was +10% at an 18, an uncommon score to say the least). Other changes to your character really didn't affect that skill in any way.
Because of this, build choices were very limited. There is an EXCELLENT thread on the boards right now about the old L&L columns that has demonstrated this. I believe the thread author found something like 6 character choices necessary to build an AD&D character. What does this mean? Outside of the features of the class (like hp, backstab, turning undead), the tactical role of a character in combat was unconstrained. Take a fighter, for example. In AD&D, a fighter had the ability to wear armor, along with the ability to excel in melee combat. This did not mean that the fighter had the "role" of defender, or striker, or anything else. What it meant was, the fighter had the ability to, depending on the circumstances of the adventure, use tactics that would fit a variety of circumstances. If my party was about to face a kobold army, the fighter might dress in plate mail and shield and try to prevent the kobolds from meleeing the squishier characters. If we are sneaking into a fortress, the fighter could wear lighter armor and wield a larger weapon. Or, the fighter could use a strength-bow and light armor, to be a mobile, ranged combatant. In a game where gp were xp, tactics varied wildly from encounter to encounter, as many groups played to maximize profit and minimize danger. The fighter had no "role" outside of the limitations built into his class (which were specialized, like not healing, and few).
Move to the end of 2e (during splatmania). The designers were beginning a process of unifying the mechanics of D&D. Now the various dice rolls to determine success would be more similar, based off of the same kind of roll with many of the same contributing components. By 3e and 3.5, the process had created a game system that was remarkably unified (d20 rolls versus DCs for just about everything). It also, by consequence, was very synergistic. Because the mechanics were so intertwined, a change in one feature of the character might cascade into many different rolls and bonuses. In addition, the number of character choices skyrocketed (I believe the other thread counted 16ish). Now this synergy meant that there were multiple ways to increase the bonuses to any particular roll. So, as players made choices about their characters, the characters became more adept at rolls based on those choices (Because what good are choices if they have no effect? That's actually not true, but a very common question/attitude nonetheless). Soon, especially by mid-levels, this synergy had produced bonuses so high that the non-specialized cannot even think of attempting things that he has not purposely built for.
Let's take 3.5/Pathfinder (because PF is the last game I played regularly before 5e, and it's pretty much 3.5 on steroids). Let's say you want to play a character who grapples his opponents in combat. You cannot simply decide in the middle of a combat that you want to grab an opponent and have it work. Why not? Because the mechanical synergy works against the changing of roles. You see, as characters level, they gain more bonuses. These bonuses (from feats, ability scores, and other character options) can be (and most often are) directed to maximize one portion of your characters combat "role," at the expense of the others. If you pick the right feats, you can have an AC in the mid-20s by 3rd level. This will mean that, by not picking other feats, your damage may be much smaller than another character of the same class, while his AC might only be in the teens. So back to our grappler. By mid-levels, the scores that are needed to grapple tough opponents have risen so high that you must invest many of your character choices in grappling in order to be effective. This means that you will not be effective when trying to do just about anything other than grappling (play with a grapple-monk for direct experience of this). When you face foes that have not been built to have strong defenses against grappling, you will defeat them with ease. When they have been built to oppose you, another non-grapple invested character will have NO chance to grapple them, because the number needed to do so is extraordinarily high. Thus were combat "roles" born!
Combat roles are the direct consequence of unbounded bonuses. When a system is synergetic and unbounded, investment in some mechanical benefits preclude increasing other mechanical benefits. This means that some mechanical effects quickly become ridiculously easy to accomplish, while others not invested-in stay the same difficulty. As a result, when challenges are created to test one mechanical effect, they must have an extremely high roll in order to make them challenging for the specialist. This removes them from any chance of success for the non-specialist in that area. So, as a consequence, most characters are specialized for their combat "role", with much less utility outside of it. Varied challenges are accomplished, not by the same character, but by having a wide build-diversity among your party. And woe unto the party that doesn't have the specialist for any particular monster (TPK).
Now, I'm going to take a brief digression to address the length of this thread. It has 100+ pages because, so far, it hasn't been a discussion. For some reason, various posters who are fans of particular editions of D&D feel the need to tell others about that edition and how it is misrepresented. Telling is not discussing. It is also irrelevant to this topic. I don't care which edition you love. I don't care how 4e is played, what the rules are, what roles "really" mean to those who play it the "right" way. This isn't about 4e. The only tangential connection between this thread and 4e is that, as a mechanically synergistic and unbounded edition of D&D, it has some similar features to 3e, in that characters can be built to maximize their effectiveness in performing some combat mechanics (about 18 choices per starting character, as per the other thread). That's it. You can love 4e all you want. You can get a full-body tattoo of the rules if you want. Awesome. Enjoy the heck out of it! But 4e has no bearing on the basics of this discussion. So, the next time you get the urge to press "4" then "e" on your keyboard, just remember that I DON'T CARE. This thread (and my argument) is not about any other edition than 5e (Look at the title of the thread, eh?).
OK, back to the essay. So what relation does 5e have to mechanistic combat "roles"? Well, 5e's bounded accuracy has made the equation quite different. Although still synergistic, bounded accuracy means that this difference between a character who has invested his many fewer mechanical options (even less than the 13 choices noted in the other thread, because some of the background choices have no mechanical effect!) in a particular set of abilities does not have a dramatically greater chance of succeeding than someone who hasn't. A character with a 15 AC (medium - Chain shirt plus a Dex bonus) can "tank" if needed almost as well as an AC 18 (heavy - plate mail or chain mail plus shield). They do not have to build/specialize their character in order to use a particular tactic, unless that tactic is reserved only for a specific class (Dirty Trick, etc.). So what had been "roles" based on the mechanics of the game, have now become "tactics," to be used by a wide variety of characters based on the circumstances of the combat and not on the choices made by the player when building the character 10 levels ago. So, like the first editions of D&D, characters no longer have combat roles based on the mechanics of the game. They have classes, which grant them some abilities other characters might not have. Everything else is tactics.
Woah! Stop! You started to hit the "4" key... I saw it! Remember, I don't care. This isn't about any edition other than 5e. To effectively disagree, you need to establish that the mechanics of this game require a player to build his character, through mechanical choices outside of his class, to accomplish a specific set of rolls in combat or be completely ineffective at them because of the mechanics of the game system. He must BUILD a "striker" or he cannot do effective damage. He must BUILD a "defender" or he cannot face opponents to restrict their movement. Otherwise, there are NO ROLES in 5e. Just tactics. Period.
