iCloud backup much too large and disconnected from what it contains

My partners ipad backup is 14Gb despite deselecting everything but 100Mb or so in the apps list. Her phone backup is 18Gb with similar settings. This in an effort to reduce usage on iCloud. Essentially it won't reduce no matter what we exclude.

The backups have both been deleted and re-created.

Proof that the backup size is a lie is given by the fact that a full backup takes 5 minutes. Which is of course impossible on out network.

Is this common and how do we reduce the backup size?

Thanks