Lucky_Blues, you are correct that you only get a small subset of the metadata online... IF you are going through a browser. However, if you are on a Windows 10 computer (not sure if it also works on Mac or older versions of Windows), you can add your OneDrive online, then you get access to all the capabilities and metadata visible through Windows Explorer.
To do that, you don't have to sync the local folder and pull down possibly GB of pictures, but you do need to pull the individual image down temporarily from the cloud. You can do this by double-clicking any image or going through several in an image viewer or slide show -- after any image opens, the OneDrive icon will change from a cloud to a white circle with a green check (this means it's temporarily available locally, solid green circle with a white check means it's permanently sync'd and stored locally). At this point, you can edit all metadata, which will sync to the cloud, and then the file will leave your local drive after a while on its own or you can right-click it and select "Free up space" to force it to leave right away.
Note that "Date Taken" appears both in the browser view and the Explorer view, but it appears you can't change it through the browser (I think that was your point). You can only edit Date Taken through Explorer.