My concern with backing up iCloud Photos with anything but Apple Photos is that there are some proprietary formats like Live Photos and slow mo video for which exports are lossy. Also, Apple Photos stores all edits non-destructively, so 'flattening' the edits into a single file for export is also a lossy operation.
It seems like an obvious improvement for Time Machine to support full backups while using optimized storage on the primary system.
It seems like an obvious improvement for Time Machine to support full backups while using optimized storage on the primary system.