If the FTC considered this material information, they should have asked to review it back then. If they requested it but Meta didn’t provide it, then it is an issue.
However, if the FTC didn’t consider it important at the time of the merger, it can’t go back and argue that something is valuable because the acquisitions turned out to be more valuable.
For example, if India and Brazil decide that WhatsApp needs to be able to see messages and break e2e, WA instantly becomes less valuable.
Or Snapchat could have eaten IG’s lunch.
Would FTC still have made the same argument?