An alternate fix would be change the kill credit system which is the root cause here. If you hit the mob and it dies, you get your credit. Make is similar to NM/Fate credit system.

Party does less than 10% damage - Bronze effort, 15% chance of feeble light and 25% XP.
Party does 10% to 30% damage - Silver effort, 30% chance of feeble light, 10% chance of gentle light and 50% XP.
Party does more than 30% damage - Gold effort, 50% feeble, 20% gentle, 5% bright, 100% XP.
Actual numbers are my suggestions and have no expectation of being used.

No more splitting credit that is currently in place. This will help both light farming and XP chain values.
There are many complaints around these forums about AFKers not helping spawn NMs because there is almost no incentive reason to bother helping out. Unless your whole party is strong enough, you will get absolutely nothing for your efforts, so, why bother.