All of those characters have long range capabilities or ways to close the distance safely without risking their own lives(aside from venture who is in the same trash category as Reaper because of it). Not to mention relatively easy to land and consistent burst damage.
They refuse to give Reaper a new ability and without one, he is incompatible with this format.
Those characters aren’t threats to Reaper, but the same is true for the opposite. Zarya is only ever a threat if she has her bubbles, but with the added burst damage it’ll be much harder for her to contest him if you time it right because he’d be able to shred her down much faster.
Doom has no counter to Reaper, since Reaper isn’t squishy (enough for to doom to kill him easily).
His damage is not great. Even if you land every pellet on the head (which you’d have to be within 1m to do), he still does less damage than a Hanzo can do from any distance (216 vs 249).
One version is a more busted version of his former tanking busting self and the other sucks because it’s just how he is now.
Aside from being a supremely niche situation in which this variant would be useful, this would leave you stuck in the backline with a relatively useless Wraith that wont get you back to the safety of your team.
It’s gutting a large chunk of the complexity in his kit for engaging the select few characters with bad self-defense abilities.
This is what it’s supposed to do. It is extremely useful for map control and getting short-range picks which is what Reaper struggles with currently, since he can’t have his damage buffed without becoming a tank buster and they don’t want to give him a way to close the gap. Giving himself a deployable advantageous environment solves a lot of these issues in the least problematic way.
Not to mention that it can even used as a bait tool in which you play mind-games with the enemy by making them question whether or not you’re actually in the smoke.