They're right.

If DOJ bans all pay for default deals, it benefits Google. That means Google does not have to pay tens of billions anymore. Meanwhile, people will still seek out Google as the default because it's the best.

Imagine if you're Mozilla. You have to set a default search engine. But no one can pay you. So what do you do? You set the one that will provide the best experience, which is Google. Only now, Google can't pay you anymore. Win for Google.