it seem like the perks at 10, 15 and 20, are meant to mostly punish players, which makes no sense at all, all their gain should be good , (some perks could be better than others yes,) it its really bad to level a thrall to get punishing perks such as - str and -vit , (dunno why they did this) funcom should let people reset thralls levels and perks… via a potion. it would fix a lot of problem and will allow to re roll those thralls once they are leveled up again.
in most cases people get angry at those thralls when they level up and end up having really bad perks, but most people will never delete the thralls in question cause they are leveled, what most will do, is just deploy a new one , this is fine but during the years, the end up pilling up in large quantities, and just used as guards .
with potions most people will likely reset their thralls and start again, (without the need to redeploy a new one) . being said that i think the thrall system needs a revisit, just remove any - negative effect from some of those nasty perks that seens to become quite common.
have a nice day.
EDIT : the potion thing will be quite IMPORTANT now that its planned to put limits on how many thralls people will be able to put in place.