iPad shows the same amount of storage after deleting backups

No, it’s because iCloud backups are incremental; there is only one backup, that is updated with changes for each new backup. It does not create a new backup each time it backs up. Just one backup of your phone apparently uses 5 GB.

a backup of the storage of an ipad is not stored on the ipad it would make no sense, it would be stored on a computer it's set to backup or stored in icloud

How to back up your iPhone, iPad, and iPod touch - Apple Support

deleting backups stored in icloud or on a computer will not give you more local storage on the ipad that you had back'd up