You need a remote service that keeps backup readonly. You’re not covering attack scenarios if you just use raw object storage from your client machine.
I'd classify that under "ease of use" - you can do it with S3 yourself (your post is a pretty good explanation of the how, from a quick skim), or you can just use tarsnap and not worry about it.
You can see from my post that doing that _properly_ is quite convoluted and requires a good deal of technical skills.
So it's not just ease of use. It's actual _functionality_ to me - getting from raw object storage to a fully working, attack-resistant backup strategy, is not trivial; hence, comparing tarsnap (or rsync.net, or borgbase, or whatever) to B2 or S3 makes little to no sense.
You _could_ compare it to crashplan or backblaze personal backup if you like, but IIRC those don't work for *nix systems, only for Win and Mac.