Contagion Problem - Why Make it Single Target?

I have a bunch of experience with Contagion in POE1, and I welcomed the change to a single target mechanism in ACT I. With GGG's obvious new theme of "swarm with super-aggro mobs and block movement", Contagion use becomes very hard to use correctly. Contagion+ED is a great combo and seems to work very well, but mousing over a target and casting Contagion will usually not cast it on that target. So here I am trying to spread C+ED, but it just keeps casting on random mobs instead of the one I'm mousing over.

I don't really understand the point of changing it from AOE to Single, especially now that I've spent a lot more time with it. Seems like even changing it to a much smaller AOE, or a larger AOE and less damage, would make this a much more manageable rotation. Or find a way to make it so the target I'm mousing over is actually the recipient of the spell when I cast it.

I've tried using it and was never able to make it proc on targets. So it sits as yet another useless item in my stash.

Little bit of a bump. This is still a really annoying problem. Again, with the style of the game being 'swarm the player with fast aggro mobs', trying to get your Contagion+ED+Curse combo off on a single target is very, very difficult. I find myself thinking "woah, sweet!" when Contagion(C) actually hits the target I'm selecting.

Here's how the scenario goes for 99% of my deaths: Mobs run towards me, I cast C, it hits a target behind the one I'm targeting. I cast C again, it misses again. Now I'm surrounded or running away. Maybe I try to cast ED on something to just get damage going, but it kills the mob and doesn't spread. Any slight variation of this where I can't get my combo off, and now I'm dead. It's literally the only way I die, and when you add in the mechanic that makes entire portions of the map respawn at death, and the slow pace of the game, it feels really bad to die simply because of a wonky spell mechanic. C already does such little damage, I cannot imagine why it's so hard to make it an AOE instead of single target. Even with increased area of effect, it's still not hitting the mobs I'm targeting.

It's very frustrating since C is the linchpin for this entire build.