Reaper is only in a good spot right now because all the heroes that were weak due to McCree, are viable again. It's the meta shifting.
The biggest vulnerability that Reaper exploits is an uncoordinated team, just like any other flanker. The difference between Reaper and Genji/Tracer is that his killing potential is faster and higher. So you kill more key heroes before the enemy has time to respond.
I was rank 70 and my group was playing against players from EnvyUS and one of the top Korean players. While it was satisfying to kill Taimou on Tracer a few times, my Reaper quickly became useless because they had 2-3 Tracers instantly pop to my position the moment I get one of the two healers. Needless to say we got our ass handed to us.
As for Roadhog, there's a balance of the heroes Roadhog are strong against. All the flankers are weak to Roadhog because they can get hooked fast. But you can harass from a distance or drop a pulse bomb after building charge from harass.
But to really answer your question, the hero that can effectively handle both Reaper and Roadhog in this meta is Soldier 76. Or with a good lineup, Pharah.
You can still kill Reaper as McCree, you just need to damage him from range. Then when you stun you go for at least one headshot before he goes wraith.