Messages size different on each device even when synched to iCloud

I have an iMac, an iPhone, a MacBook Pro, and an iPad. I have messages set to synch with iCloud on all 4 of them using the same Apple ID. Each one shows a different amount of storage taken by messages - from 4.42GB on my iPad to 14.3GB on my iPhone. My iCloud storage shows messages taking up 25.3GB. Why don't these match and what doesn't synching seem to do ANYTHING at all? I spent a lot of time deleting message attachments on my MacBook, just to see it didn't save me a bit of space on other devices. Does Apple really have this so screwed up that I'll have to go through and delete messages and attachments multiple times on multiple devices to try to get down to one amount across the devices?!?!?!?!?!?!?!?!?!?!?!?! How is it to have something you call synch when there is absolutely not a **** thing synched between any of 4 devices or iCloud.

Please help if you have any insight into this oversight of Apple's!

[Edited by Moderator]