Most of those mistakes are because of passing, something Merc don't have to worry about off the front row.It's not the car that turns right into the grass at the start in Australia and breaks the wing. It's not the car that tries to hold off Hulkenberg when he's a sitting duck, and clumsily tags Hulk. It's not the car that makes a failed move on Kvyat in Azerbaijan, then backs into him in a panic. It's not the car that makes the desperate move on Norris and fails. It's not the car that's on the right edge of the circuit behind Raikkonen, then decides to turn right off the track.
His situational awareness has been crap. And all it's doing is making him look silly.
The MB would be a better car. But there's more tension and more at stake when you're around the others, particularly your team (Even Bottas).
At RB, the psychology is easy. You're not under threat from the 4th best car for the season. You can go all out, and typically it's the other car that has more at stake in the passing move.
Sure they're mistakes by him but those same opportunities aren't there for the 2 x mercs.