I understood part of your situation up until this part:
"...what I typically do is move files directly from the device folder in the folder pane directly to the folders on my local desktop catalog. In the end, the device folders are empty, and the photos are locally stored. What i've noticed, however, is that doesn't eliminate the photos as synced photos, and right now I have a large asymmetry between the collections I have synced between Lightroom Mobile – a handful of a couple hundred photos – and the "All Synced Photographs," which is nearing 7000 photos."
Can you rephrase this or clarify your current process? I just want to make sure I'm understanding the situation correctly to help you.
Maybe easier to illustrate.
Here is what is actually displayed on my devices:
My workflow is to move photos off these device folders directly into my local photo library on Lightroom Desktop. These folders are pretty regularly pared down to zero. Here is the list of synced photographs I have in lightroom - on Lightroom mobile and on desktop when I am signed in with my Adobe ID.
I don't want 6000+ photos synced via lightroom. Instead i want to use lightroom mainly as a passthrough to automatically upload my photos/videos from my various iOS devices camera rolls – and sync selective collections over.
Those photo collections under "From lr mobile" don't match the "All Synced Photographs" above. Neither does it match the collections – or device folders that I have displayed.
What i'm looking for is a regular workflow in which "All Synced Photos" matches only what is synced via collections and devices, and nothing else. What it looks like to me is that lightroom continues to store thousands of my photos long after I moved them off the cloud and into my local backup. The "from Lr mobile" collections are actually referencing locally sourced files.
What does "delete all data" mean? If I temporarily stop syncing my "From Lr mobile" collections and then flush all the data using the "Delete All Data" button, and then resync the collections, will this get me to where I want?
thanks for your time,