#1 Why does there need to be a plaintiff? A trust affects consumers and society broadly detrimentally, not some specific competitor. The competitor google is likely trying to suppress is some theoretical startup anyway, they probably don't exist to sue.
#2 Why the focus on specific damages? The specific harm of such a trust are inherently unknowable.
The Google-Apple deal isn't new, and has been widely reported on. Google pays more to apple than 2nd place (MST/YAHOO) has ever delivered in topline revenue. Apple can (a)take pure profit with no effort or risk, (b)build a competing business with much worse best-case prospects, or (c) leave room in the market for someone else to try. It's not really a choice.
Meanwhile, Google's largest investments (eg chrome, android) are just an insourced version of the Apple-Google trust. Monopolistic deals and strategies aren't a side-show, they're the primary activity of these companies.
To me, it's increasingly obvious that monopoly issues are structural. It's not what Google/Apple do, it's what they are. Dealing with antitrust in an infraction->lawsuit manner, post facto, is a designed to fail structure.
IMO there are two choices, besides just accepting the prevalence of monopolies, cartels & trusts. (1) They can be broken up. (2) They can become "regulated monopolies," with a regulatory structure designed to prevent monopolistic harms before they happen. Yes, it will harm their profitability.