I agree with Ginnel. It is only punishment when you continually club your players over the head saying "Don't you wish you'd picked a different class? Hahaha."My 4E party is very striker-heavy; out of six characters we have four strikers and two leaders. Hence, I don't include challenges for defenders or controllers. I don't clog the battlefield with minions since there is no controller to blast them away or a defender to wade through them with a melee weapon. I give the party combat challenges where they have to fight high hit-point monsters to accomodate all those strikers. We still haven't had a character death (although we've been close twice), and no one has noticed a shortcoming in the group. I'm not going to "punish" players for not wanting to play defenders or controllers.
A fight that is against 6 soldiers and brutes would be punishment. But, a fight with four or eight minions would force the party to change tactics. Because they are strikers, the party can easily do "Hit and Run" type encounters.
Furthermore, with two leaders, the party has a little more staying power. An encounter that is a controller and a soldier with several waves of minions showing up would be an interesting challenge.
To use 3e terms, if you have a party with rogues, clerics, and wizards, a golem is a tough enemy. However, if you give them a little for-warning, or engineer the encounter area, the fight rewards creative thinking and spell usage where raw numbers don't work. Relying on summoning creatures to create a "wall" while you exploit the golem's weakness, or using force walls to block it while you move around it, etc.
Designing an encounter that hammers a party on their weakened role is mean. Designing an encounter where the party has to adapt around a missing role is engaging and interesting.