As you get higher in arena or in maps , the scaling on dots/necrotic damage simple scale too high. Often you can die with 50% res in a fraction of a second from the plants poison aoe and from the mobs that do aoe necrotic damage.
This punishes melee characters much more , as they tend to be closer to the action.
It’s worth noting that the percentages are not actually damage reduction in the typical sense and can be misleading. The percentage represents your effective HP increase from the resistances you have however they scale with your total health, the actually important bit for comparing is each protections value. It is sort of like a health pool that only works against one damage type but does not need to be healed.
In other words the higher your actual HP/ward total the lower the percentage will be for the same amount of resistance. Thus 50% ‘resistance’ on a 400 HP pool is really only giving you 600 effective HP (and the percent comes the actual protection value compared to your maximum HP) so if you stack poison up high enough or take a big enough single hit then you will 100 to 0 instantly. Similarly, if you stand in stacked AoEs then you can and will suddenly take a stacked tick of damage higher than your HP + Ward + Protection for that damage type.
Poison specifically can be a serious offender due to poison increasing 8% per stack so in a sense each stack is double dipping; increasing the damage due to adding more stacks but also increasing the damage from all existing stacks by that amount.
I think the main issue is that DoT has no mitigating factors like block/dodge/glancing blow/critical avoidance, it’s all on the protection/life pool and we all know that that isn’t enough for survival or we wouldn’t build the aforementioned stats. Just the fact that glancing blow doesn’t help against DoT means you take double damage from DoT compared to hits.
And, I’ve felt a shortage of necro/poison protection in the passives/specializations. I see elemental and void protection everywhere but it feels like the only place I can get necro/poison protection is on gear, which means giving up other stats for those affixes. Of course, even after having those protections you still die in 1-2 ticks.
Hell, earlier I died to a boss because he dropped an ice maelstrom totem on top of me from range and I died before leaving its AoE.
The easiest counter to DoT in health regen. Stack alot of health regen and it inversely reduces damage from DoT. I run several characters with 4-500 health a second regen and they can stand on Void spikes until wave 100+.