If you Data is not on media you own, it’s not your data anymore.
True.. But I encrypt the folders that I share with Dropbox, Mega and Box (except a few that I wish to have publicly available). That way, they can look at all they want they still not gonna see anything unless the encryption is broken.
If your data is as local as you can have it, but you run W10, then it's not your data either and MS can ship it off at a whim for a looksee if you're online, at least with the home versions (read the EULA if you doubt me!)
If you keep your backups online (powered up and attached to the machine) they are not backups. Every few years as the price point comes down buy larger disks, copy your data, and put the old disk in the equivalent of your socks draw.
Owncloud, Box, Mega and many other cloud servers provide for retrieving older versions of files (at least so long as you haven't cleaned out the old versions cache!). As you say, keeping them online is a risk but at least with the ability to get older versions, there's a good chance a good copy is still around.
(I have old disks going back at least as far as 2002 - not sure if they'll still work).