For the record, I'm happy to live in a world where rsync.net exists. I've pointed quite a few customers in your direction over the years, when tarsnap hasn't been suitable for their needs for a variety of reasons.
First is that my usage of Tarsnap pre-dates my usage of rsync.net so it's been the primary backup of my home directory since ~2010. I haven't felt a need to change it and the 2 occasions I needed to restore it everything worked perfectly. i.e don't fix what isn't broken.
The second is that while I can in theory restore from rsync.net I actually never have... this is more a testament to the relability of ZFS though I guess and local snapshots have always been enough. That said the convenience of send/recv is sort of awesome.
Lastly is that I don't use ZFS on my client machines. If I did I would probably consider rysnc.net for everything.
So it's not really an explicit I think one is more secure or durable than the other it's that Tarsnap has fulfilled my DR needs successfully for a long time and I have come to trust it to do so in the future.