More competitors in the advertising and search space would certainly help, or at least keep the situation from getting worse.
As for Amazon, the antitrust enforcers should have come down on them like a ton of bricks the moment it appeared that they were leveraging internal business intelligence to compete with their own sellers. I use Amazon constantly, I have an enormous amount of respect for them, and I value their services a great deal, but come on. There's no point in even having antitrust laws if they don't apply in this instance.