People often complain that vahzilok are overpowered at low levels. They are not. You just have to know how to fight them, particularly prioritizing which to attack and cc. Experienced players know this and can defeat them without difficulty.
The cadavers are resistant to several types of cc but they are easy to knockback and more importantly to slow. They move slowly, so you can use your powers to keep them from reaching you. What works great against them are the various rains that do damage and slow. Also aoe knockbacks like storm has with its wind powers like gale. And stunning them works well.
Mortificators can rez the cadavers, even though the mortificators themselves are not as damaging. So kill mortificators first.
The reapers are weak. Basically ignore them and kill them last.
So to sum up, when fighting vahzilok: seasoned players don't fear the reapers. They use wind, stuns, and rains. You can be like they are.