An old friend of mine who had to leave our gaming group for various reasons recently returned. He created a new character since we had gone a long way since he had left and he wanted to try a defender. He put together a Warden and joined our group. He optimized the character's health and healing surges so that the character could survive, and he did a fantastic job at this. The character is insanely durable and I won't ever kill him without him doing something overwhelmingly stupid.
The problem is that his character has basically no role in combat. Wardens struggle to remain sticky and he has done nothing to make up for this. His OA is so weak that enemies can simply walk past him to get to the rest of the party. He hasn't added anything to his mark punishment, so enemies freely attack other party members with only a -2 attack penalty to deal with. As a side note, the character does roughly 9 damage per round at level 15 (effectively nothing, for those of you who don't play 4e.)
I tried subtly noting that his character wasn't the stickiest, and he responded with something along the lines of that being the warlock's job (that's our party's controller because no one in our group ever plays a controller) and then read off his healing surge nonsense for the umpteenth time. I think he doesn't understand the defender role and that's the root of the issue. This is his first "power-gamed" character and he's quite proud of it, so how can I tell him that the character isn't filling the defender role in any real capacity without causing any conflict?