The issue with this is that you inflict unnecessary punishment on anyone who may not be the best at the game and easily run the risk of Castrum & Dalriada becoming dead queues for people genuinely needing them. if Dal only gives 3million for a clear and someone isn't very good and knows they'll die enough times to get negative mettle from the whole affair, why would they queue? This exact issue was present before they made Castrum give tons of mettle for clearing due to the rewards not outweighing the losses. Not to mention any mechanics where others can kill you with no input on your own to stop it (Tank not paying attention in the final boss of Dalriada and baiting tank buster laser on people, not enough people stacking for stack markers and causing you to drop dead out of no fault of your own, Lyon group fails to beat him thus you die due to their incompetence, one side of the 1st boss of Castrum wipes so you die due to no fault of your own, etc.).
Not to mention such higher risk of dying just forces people to gravitate towards tank classes anyway or only using defensive essences/actions rather than offensive ones/jobs, making your runs even slower. Why play a dps with such harsh penalties when tanks + essence of the guardian have like 4x the survivability power? Why bring lost font of power when you can bring lost cure + lost bubble and constantly heal yourself instead of dpsing to make sure you survive things better?
You can't implement punishments that affect more than the sole target meant to dissuade them. it's the same logic as all those people wanting harsher leave penalties: They'll do nothing but hurt the innocent than your intended target. Since DR has no loot that has timers, the far easier solution is just allow people to kick & refill parties in there, and allow people to kick someone that isn't in a party. Done. CLL & Dal are a bit more complicated, but they could implement a check at the end of the instance that checks to see how much enmity credit you did during all the bosses and disqualify you from loot (including relic items & mettle) if you did less than it. But make it a very low threshold so that way only someone only autoing or afk could possibly hit it.