That could be said for Facebook surreptitiously uploading images by piggybacking them onto innocuous requests.

I’ve disabled the FB app’s cert pinning so I can MITM it and they really don’t seem to care about minimizing the number of requests. Tons of little logging events will be fired off separately instead of being condensed. Also, there are several unofficial Instagram apps that were developed by thoroughly reverse engineering the app’s private API. Seems unlikely that this could have evaded detection.

And just data volume-wise, it’s much harder to conceal uploading weighty images/video. Facebook and Instagram mostly just download data. A long term discrepancy in upload usage between when the app has camera permissions and when it doesn’t would be easy to spot.

I have no doubt Facebook is still doing creepy things we don't know about yet, but this particular theory just seems incredibly unlikely to me.