Hey Gavin,
As you mentioned, the Facebook Ads source is a Cloud Object source. Cloud Object sources send records/Objects rather than individual Events (page/track/identify calls, etc). These Objects are generally batched together. This affects the number of API calls and Object sends directly via your throughput. You can check out this section of our docs for more detail.
The number of Objects that you can send from Facebook Ads before hitting your throughput limit will also depend on if you have other sources sending Events or Objects in the same workspace.
For more granular info on your specific use case, I’d recommend reaching out to your account team.