This is probably going to have a lot less effect than what people are assuming it will have.
Google and Facebook have never had more competition in the Ad space. Apple and Amazon are building big Ad businesses fast. That's not the problem. The problem is they play both sides of the market and they dominate both sides of the market. Therefore they have a lot of pricing power.
This isn't the reason they are making 100s of billions a year. The reason they are making that amount is because they are the best at what they do and you can't find the service they provide any where else except Facebook and Google.