To anyone facing this issue, here's the solution:
** Mange sure you download / have a copy of all your iCloud Photo content before following these steps since this will clean up all of it**
Under "System Preferences", click "Apple ID". Select "iCloud" on the left-hand panel and click the "Manage..." to manage your iCloud Storage. Select "Photos" on the left-hand side and click "Turn Off and Delete...". Once this is done, re-enable iCloud storage for photos within the same menu itself.
Only by disabling/enabling Photos on the prior menu itself (Apps on this Mac using iCloud) won't do the trick and your iCloud content will persistently reappear. Trying to delete photos solely from https://icloud.apple.com also will not do the trick. The only reliable option to get rid of all your photo content from iCloud seems to be using the "Turn Off and Delete" option as described above in my post.
Hope this helps other users facing this issue.
Regards,
Rick