To OP. One of the issues our group had transitioning to 4e was to lose the pre-4e mindset. In pre-4e there was only really one great measure of success...damage! A single identifier of whether you had an on-par (OP) character (disclaimer : Might not be that extreme, just my experience with pre 4e). Its easy to recognize good damage.
Once 4e came out, character had roles. You have introduced the first striker the the group whose role IS to cause lots of damage. One of the challenges your non-striker characters now have is to recognize non-damage contribution for its worth.
We have a level 21 party.
The tank can lock down near any number of monsters. He does (relatively) bugger-all damage, but he is super-hardy and takes great pride in filling his role. He doesnt care about his damage output, he knows when monster are attacking him, he is wasting their time and doing his job.
The warlord has multiple heals, multiple groups heals and even more utilities to aid tactical deployment, initiative and buff up action point rounds. Does pitiful damage, but the player still regards this character as the best he has ever played in any RPG (and I have been with this group for 20 yrs)
The mage (who admittedly does very good damage, darn bloodmages) in one battle blunted 2 charges from 2 separate directions in one round, then in the next round proceed to stun 3 lvl 21 demons. Major contribution = party fought 1 or 2 creatures at a time...not 15!!
Just have the monster focus fire on your thieif, then watch the tanks have to draw it away, the leaders to have to heal him back and the controllers to bring an end to the barrage, and they will figure it out.
(p.s. Our party strikers are regularly doing 100-200 pts per round at lvl 21, for which I congratulate them, just as I congratulate the non-strikers for a job well done)
