> like taking a photo, assuming stuff is sent to this service immediately upon adding a new photo

So you jumped to a conclusion based on an incorrect premise. This is easy to see that this does not happen immediately after taking a photo. One the network traffic will show this (and it won’t), two homomorphic encryption is expensive so it cannot. Photos classically doesn’t sync on demand, as most iPhone users will know by way if it telling you this in the photos app when it does sync. Most expensive operations are queued up for when the device is plugged in (and on WiFi) because it’ll otherwise drain battery.