Free space in iCloud not less even after having deleted all files in iCloud Drive
open system preferences and click on icloud. a new panel opens as shown below. click on the option button next to icloud.



After clicking the Option button a new panel opens. At the bottom of that panel is a checkbox to optimize mac storage. Make sure that box is unchecked.  See 2nd figure below.



If the new icloud space doesn't look correct give it a few hours to update.