I used OF for years, and don’t think I ever looked at that date, because it doesn’t really tell you anything you don’t know. Ie if you see something hasn’t synced, you really only have one choice, ie, get your devices online so it can sync. A date is not going to tell me much, because sync is a very complex process of uploading and downloading on multiple devices. Is the date the last successful upload? Last download? Not clear unless you have all the info, and then it is simply too complex to be useful.
Your last line is exactly the right solution here. If you see something that is “out of sync”, all you can do is connect to a network, preferably both devices involved. Seeing a date for the last sync wouldn’t really tell you anything useful IMO, other than what you already know.
But we will keep it in mind. If others request it a lot, we will think about it.
Note that for long syncs, the iOS devices should already show a network spinner to show a sync “is underway”. Unfortunately, I have noticed the notch on iPhone X seems to mean it doesn’t fit in the bar anymore