Your approach to pk seems to be that two people start duking it out.

As a necro, you shouldn't be putting yourself in this position because that's not where the classes strengths lie. You cannot play each class with the same mindset (well, most can't).

You can kill lowbie warriors with lowbie necros without using preps. I've done it myself with only chill touch. However, you aren't likely to manage it if you just walk up to a healthy warrior and start doing it, whereas a lowbie warrior is unlikely to lose to a necro if he walks up and attacks them when he's healthy. A necro need to make use of stuff like the invis spell and jump them when they are already hurt. A good way to tell this without them hearing you walk around is to wait until you can see they are sleeping. Then walk in, take a look at them, and if they are badly hurt, try your luck.

Since they are lowbies, warrior bash skill is much less effective (if they even have it), and you have the chance of landing a mean chill touch (because sometimes it does more damage).

Both of these changes are things imms put in to make magi more viable at low levels, based on player feedback.

Quite frankly, putting someone to sleep as a lowbie necro is counterproductive. None of your spells will last long enough to run them down, and your maladictions are not going to achieve much either until level 23 where you get crimson scourge.

Just because sleep is the ultimate spell for a higher level necro does not make it a good one at lower level.