Seems like no matter what lvl plague carrier is.. the parasite is still lv1?
No one else seems to have reported this on forums, or im blind and fail@search
Unfortunately I leveled my Plague Carrier to full without even checking each level's effects.
We can probably do a comparison, though.
At level 50, my Plague Carrier does 67 damage per second per stack.
I have to agree, this seems a little weak for a level 50 skill that's maxed out.