FFXI Style NPC that tank/heal if no player was founf in like... 10-15 min, even if their AI were not that good would help, even... make DPS more careful to not steal much agro or rush???? Dunno,maybe a couple of selectionable npc at start of dungeon that play different so party have a run more adapted

I'm asking for much, but yeah

Other option, less develop consuming, would be to let 3-4 dps join and give them an echo that boost their defenses or gives them regen.

Or the most dificult way to solve it: Make the community less elitist/whiny to tanks/healers that are just trying to have fun and learn, and give veterans a incentive to help new players