You can move the HomeKit hub around from device to device ... or have more than one, say, an AppleTV and a HomePod and an iPad. Encryption is by virtue of your iCloud identity ... just as Google do with encrypting Chromebooks. Yes, encryption can be broken; not least when some quantum leap in processing is made. All that encrypted traffic we thought was safe, all captured by intelligence spooks and squirrelled away for that very future moment will just be opened in seconds.
I'd also say, if it's connected (regardless of home/cloud wherever) ... connected, it's "in the cloud". Security is as strong as the weakest link in the chain, so getting in via a poorly configured random name camera with unofficial protocols running and then talking through that to, say, Alexa to then open up whatever the hacker wants ... it's all possible.
But yes, my point was about finding an ecosystem and cloud provision that suits what it is you do. I'm very little about actual files (although what I do have are all in the iCloud ecosystem either as files, but more likely as Apple Notes), big on photographs (Apple Photo ... again, iCloud), less so on music, even less so about movies ... a lot about home automation, for which HomeKit and iCloud really suits me. While I do have a Chromebook, I have literally nowt in Google Cloud but do serve out my SOTD pictures and other miscelleanous stuff for forums from Google Photos. For many folks, Facebook is ideal for communication, that gargantuan photo storage and for communication and collaboration, written, voice or video. Google have all that, too. Amazon do. Apple do, but iCloud+ is offering the next step beyond simple storage with some presently unique features.