Well thats what I thought too but its kind of strange how you dont get your killcount reduced for each dragon you kill. I have a 148kc dragon task at the moment which means I could technically do 148 solos the way it is right now.
Was kind of hopeing someone has done some testing to see if we get the damage boost, especially because tuska's wrath doesnt even work on these dragons.
If you're running with a team then chances are they're doing either more damage or you're not getting last hit.
I'll take a gander on Monday in regards to the slayer helm thing.