Back on live, I would often run missions with my friends, playing characters who were a mix of ATs, with no Incarnate powers at all - because they hadn't been invented yet - and nothing but IOs or sometimes just SOs.
The pace of killing "arresting" progress was such that it inspired the term "spawnmower".
Full teams of experienced players with fully-leveled characters tossing around cones and AoEs, buffing each other, debuffing the enemy, and exercising even basic strategy, target selection, etc have always been extremely effective in this game. Maybe not "+4x8" effective, but I hope you get my point.
Miscalculations and even wipes do occur sometimes, but this is not a game where the group has to stop and take a knee (and buff up again, regain mana, etc) after every room.