Matchmaking is based on SR, not level.
1> Scatter is deemed an issue not because of random arrows flying everywhere, but because you can shoot the ground in front of someone, and all the shards bounce up and hit them in the chest/head. The shards do up to 450 damage. Even hitting with half will one-shot a DPS or healer. They can also erase tanks.
2> Junkrat's grenades have longer travel time and bigger arcs, and only hit for 120 damage each. If you're running into his mess of bombs, you were asking for it. There's no warning from an incoming Scatter.
3> Junkrat is an area-denial guy. Spamming grenades around a corner means you should take another route and shiv him in the flank.
I have serious issues with Hanzo's design because easily 50% of my deaths to Hanzo feel unfair. It's either a scatter that one-shots with poor aim, or it's the random arrow fired at empty space that magically headshots me while I had no prior warning. It's the combination of lack of skill with the lack of warning that's the issue; a Widowmaker headshotting you doesn't "feel" as bad because she had to track you and shoot you directly, not launch and pray. Junkrat launches and prays, but his bombs are big glowy bouncy balls, and if you're running into that, you knew what was coming. There's probably not much they'll do about the random Hanzo spam arrows, though adding a better visual or sound effect to show there's incoming fire would help (as there is for, say, Soldier 76 spamming shots at a doorway). But Scatter needs some rework, since it was designed as an AoE tool to catch people hiding in rooms, and it's being used as a one-shot tool.
I have no idea what their rework ideas are, or how deep they're going, but assuming he keeps the same abilities, increasing arrow flight speed significantly and changing Scatter to only hit a given target once or twice would be a big help. Increasing arrow flight speed A> makes it easier for Hanzo to fight at a distance with good aim, and B> means it's WAY less likely he'll spam a corner and hope your head shows up before the arrow gets there.