About this, I am trying to avoid storing any of my mnemonic phrases online, all are only offline.
Another thing is store it also in multiple places, and the one down side of this is the risk will be higher if you store it on multiple places but at the same time you have more back up, just make it safe to be able not be access by other people.
I think two places for two backups are enough as more places mean more risk. I agree with you that wallet seed backups should not be stored online. We can not trust third parties as well as there are more risks online than offline.
I have more than one wallet because store all money in one wallet is not good and my main capital is stored in a multisig wallet, not single signature wallet.