Why is iCloud syncing such a disaster? How can I fix?

I have two Macs and an iPhone. I have a separate iCloud account (separate from my iTunes/App Store account) for iCloud syncing. Until now, I have never had this working properly in any way:

- Keychain syncing doesn't work at all. Both macs have a different set of keywords in their iCloud Keychain, new passwords are (sometimes) added to both, existing passwords do not sync at all.

- Contacts syncing does not work at all. I have a set of Contacts on my iPhone. Even resetting iCloud Contact syncing on the Mac does not get them. I finally got them because it turned out that when System Preferences thinks Contacts are synced, Contacts.app itself has no idea about that account. Add the account to Contacts.app and in your System Preferences Contacts syncing is turned off. etc.

What is needed is that Apple fixes this, also in the current OS versions. And what I need is some sort of manual to get this unstable mess in working order.

(I am clearly frustrated, I've been wrestling with this for ages and ages and ages and I have better things to do than wrestling with Apple's unstable implementation of a good idea).