If you're defending against your own government, they already control the network and could hold on to your S3 network traffic until they can decrypt it.
If you're defending against an individual how would they know where to download your file from? I assume the network doesn't broadcast a connection between real life identity and the data you're storing. And if the individual can monitor your physical network, then they can again decrypt the network traffic eventually.
If you're defending against the server hosting your content, they would have to host your old data for years past you stopping the service before they could decrypt the content, which would be a massive investment.
Finally, do you have reason to believe that our current encryption algorithms will be cracked anytime soon? The last big innovation I heard was SHA-1 generating a hash collision in 2017, but even that took thousands of dollars in compute resources, and SHA-1 was known to be defective for a long time before that. I imagine if we use our best algorithms they'll hold up for quite a while longer.
So my understanding is that in the example of a decentralized app that uses Filecoin to store an IPFS object on the network the IPFS object id could be sniffed on the localhost by something like Wireshark. This way an attacker could identify the encrypted objects that are of interest to them and then independently request them from the IPFS network.
In terms of threat, I'm primarily thinking of larger criminal organizations that might target things like files containing SSNs, credit history, etc.
SHA-1 is an example, but my biggest concern comes from the potential of quantum computing to render what we consider secure today obsolete. (https://www.technologyreview.com/2019/05/30/65724/how-a-quan...)