Controllers do much more than kill minions. They apply better debuffs more consistently to more enemies than other roles. They're better at forced movement than other roles. They're the masters of reshaping the battlefield. Oh, and yes, they also excel at area of effect attacks, which happen to be good against minions.
But to what end? Dead is clearly a better debuff than anything a wizard can throw out there. Generally when I see Wizards tossing out their debuffs it is very ineffective because the die rolls are not in their favor. First they have to hit (about 60%) then the enemy has to fail to save (45%). Our invoker blasted an entire battlefield with over 15 minions and 4 other enemies with a slow debuff only to effect less than a quarter of them. Our dragonborn defender quickly applied the 'dead' debuff to at least 5 of them, as well as drawing the fire of their leader. I noticed that the minions weren't able to make saves against 'dead'. Because of the controllers daily 4 or 5 minions were not able to make it into melee in the first round. Maybe 15 damage was prevented (leaders can do that 2/encounter as a minor). I see the controller's role, but I don't see them as effective.
You're missing the forest for the trees. Each role is so much more than you're making them out to be. Controllers directly counter enemy strategies and disrupt enemy tactics. Defenders disrupt focus fire and prevent enemies from engaging their preferred targets. Leaders enable party tactics and enhance party efficiency. Strikers engage and neutralize priority targets as quickly and efficiently as possible.
Without a Controller, a party is much more vulnerable to coordinated enemy tactics.
My point was that each of the different party rolls get a bonus to help them perform their role. Defenders get their mark (and usually added abilities), strikers get bonus dice (or similar abilities in PHB2) and leaders get their heals. These abilities are all extremely powerful and define the class. You could claim that controllers' class roles are covered in their powers, but look at their at-wills. None of these seem that powerful to me (I'm looking at Wizard atm). Slow one target, blast 9 squares for a d6... Not so great. The Sorcerer has better area at-wills (such as burning spray or blazing starfall deal more damage with the sorcerers
power class feature). So yes, the controller has a class role, but I feel that the other classes can easily 'control' the battlefield and that the controllers are not much better at doing so. No class is better at healing than a healer, no one can draw fire like the defender, the strikers are unmatched in focus fire, but anyone can do the controller's job.
In my party of 6, when we fight mass hordes of enemies, our 3 strikers quickly dance/tumble/teleport past enemies and bring down the leader in 2-3 rounds. Without a not-dead-enemy-leader, the party is far less vulnerable to enemy tactics.
Ironically, this is why I think a second defender is the best choice for a 5th party member (although I think that defender should be capable of near-striker level damage). Defenders are the best role at pulling enemies off of an ally who is suffering focused fire. If the Defender becomes the target of the focus fire, no one is better than a second Defender at pulling enemies off of him.
t~
If the first defender was a striker with a few GTFO powers, the second defender seems unnecessary. Besides, even if one of the strikers gets focused and goes down occasionally, the party still has more damage output with 4 strikers than a typical 'well mixed' party.
