if a few years ago somebody said "just copy all your private data to some place on the internet... but encrypt it first" you would take it for the crazy argument it is.
What do you think is crazy about it? If it's encrypted, it can't be read. If it's on "some place on the internet", it can only be as redundant or more redundant as any other offsite solution.
Any agent capable of ever reading AES encrypted files with 256 bit keys is also an agent capable of opening your safe deposit box, requesting your tapes from a data vault provider, or coming over to your house with a rubber hose.
Short of a vulnerability in AES (in which case we have more problems than a few copies of the Anarchists Handbook in our backup files), cracking proper encryption is simply not feasible.
With arq there are multiple layers that would have to be broken to get to the data. Still a risk, obviously - and one worth considering. I bet in the scheme of things though there are much easier ways to access this data available now.
if a few years ago somebody said "just copy all your private data to some place on the internet... but encrypt it first" you would take it for the crazy argument it is.