Guild Wars 2

I think you may be missing the point of corruption skills. If you are using them, then you are most likely condition based, lots of bleeds ect, which make the corruption skills very good.
The aim is to hit the 25 bleed cap or get very close to it which means that with blood is power followed by deathly swarm is great for stacking up bleeds.
As to “wasting” deathly swarm on one condition, BIP counts for 2 because of the 2 stack of bleed, and deathly swarm only moves 3 conditions anyway. You still have consume and staff #4 for condition removal if you are worried about survival.
The main question to ask is if you are PVP or PVE based (does not say in your post), PVE most of the time if you can dodge and work around your skills/heals, you really wont have that much in the way of conditions on you to worry about, i don’t PVP so i will have to hand off that side of things to someone else. think of the self conditions as bonuses rather than failings, as a necro you can use them far more than they can hurt you.
My condition build has over 32k Hp at lvl 80, so 1000 damage from a few bleeds i should be handing off anyway isnt that big an issue, depends again on your gear and talent setup
hope this has been helpful