Aye, I had a group wherein someone with this intention queued as a tank to get in faster. Soon as we entered and got the ability to fly, he promptly changed jobs to a DPS and ran off to tick off objectives then left. It crippled our party because we couldn't replace a missing party member and no one had a tank job leveled to do it themselves. If you don't have a full party, you may as well just hang your hat because your team cannot muster the damage required to get gold chests.

I like Diadem a lot, but I haven't been able to really play it lately. If someone else changes class or leaves altogether it really penalizes the others and not the person who caused the strife. Especially since effected persons cannot just also leave and re-queue. Reducing the entry timer was a nice start and I'm thankful for that, but it needs a few other adjustments to make it less victimizing. Dev team would know best how to go about this but if i were to wager a guess at some things that might help I'd suggest not allowing someone to leave until a certain time has passed, allow people to kick and to refill members from the duty finder queue, and adjust the amount of damage dealt on mobs to scale with the amount of battle class party members.