Balesir
Adventurer
I think you are overestimating the "need" for specific roles in 4E. I DM for a party of seven that has no Leader; two Fighters (one of whom is multiclassed a bit into Cleric, I admit), a Paladin, a Ranger, a Rogue, a Warlock and a Wizard. I use all types of monsters, with XP budgets scaled up for a seven character party, and it works just fine. Do the players need to understand their weaknesses and work to cover them? Yes, but I find that a thoroughly good thing.Well, it becomes a problem with the design assumptions of the game. The damage of brutes and artillery takes into account the fact that there is a leader available, for instance. I could not use those monsters, but that puts limits on my ability to imagine awesome adventures for the party, which isn't great.
Two aspects of 4E stand out for me as regards roles: party design trumps character design and party tactics trump character "combos". Roles feed into these features, and yet do not make the game prescriptive in terms of party mix. I find this a peerless achievement.