Keeping positive effect same wont help the trader survive. In case of high NR professions like enforcer or NT its hard to even land both drains if not almost impossible,
now you say that they should last only 30 seconds.
Oh and the whole "Like i've said before, if you are going to keep someone useless, then you need to be actively doing so.", if you are going to ignore 87% of my dmg you should atl east work for it.
Lets make AMS last 30 seconds with same duration on NSD.
The duration is fine imo, once you die/kill you remove it.