I agree with this. I don;t think she will ever get to mercy levels and at most tiers she never will be. She is a hero that requires a high amount of teamplay to work well, not to mention the individual skill of the sombra is a lot higher than pre nerf mercy was.
Of course OWL is a bit of a different beast. With the coordination and skill we see from those teams she could maybe find a spot in regular rotation, but I still do not think she will become an oppressive pick.