I have no intention of using Adobe's 'cloud' as a replacement for storing photos opposed to local storage.
I intend to use Lr CC for what, IMO, it is intended for, that is for Mobile photo usage.
But - - -
Been reading all the syncing problems posts here and I got curious so . . .
I distributed 500 photos to my computer desktop in a folder, some to an external (USB-3) drive and some to a USB-3 thumb drive.
I then started an Add process using Lr Web for some of the files, switched over to Lr CC desktop and started an Add for the rest.
Then I watched the sync process from within Lr CC desktop. The entire sync time was about 5 minutes. Sync hung with 11 photos to go. I paused then resumes sync and the last 11synced in a flash.
No point to be made here other than the Adobe sync system seems to work as I expected.
Oh Geeeeze! Now I get to delete 500 images from the 'cloud'. Another test?
Noted no 'select all' available in Lr Web but Lr CC desktop allowed it so I deleted from there. Took less that a sec.