Any character you chose can be overpowered, but to another person that character may not be that overpowered.
Like if someone says Bastion is overpowered, well yea he is, but get a Genji up in there use his 'e' move and just deflect all the shots back at bastion, since Genji is a direct counter to Bastion is works out really well.
Both very true to be honest, I've noticed that turrets can be shut down so easy from the rocket person and sniper ( need to get more familiar with names! ) every hero has their own weakness.The game is very balanced IMO. There's always someone who can counter another hero.