This thread has become so full of salt 
#ReaperIsTheNewMercy?
But to answer your question OP, Reaper is currently stuck between two niches. Is he an assassin, or a brawler?
Someone in the devs’ office can’t quite decide what Reaper should be, so as a result he’s mediocre at both roles.
I believe he needs to find one role, and stick to it well.
SHAMELESS PLUG! I have suggested two different ways to make Reaper a little better at one of those roles!