The only verification data you need in this case is the hash from EIP-7643, namely 0xec8e040fd6c557b41ca8ddd38f7e9d58a9281918dc92bdb72342a38fb085e701 .
This hash allows you to verify proofs.txt which in turn allows you to verify the rest of the era archive (strictly, proofs.txt shouldn’t be needed either, but I suspect it’s convenient to have it to make the process of finding errors in the files more fine-grained) - there exists no benefit whatsoever of getting this file from a separate source (as long as you have the above hash) - it belongs inside the torrent.
This is also the problem with the idea of using a torrent, which is why it’s somewhat unattractive to clients: there is a structural mismatch in the verification mechanism used - the hashes of the torrent itself don’t line up with hashes used in ethereum, which is why we need proofs.txt to begin with - this makes partial verification somewhat involved (because as you’re downloading the files in the torrent, you need to verify both the torrent hashes and the ethereum proofs).
That said, I do believe there’s utility in socially coordinating around a single torrent file for convenience of testing, if nothing else 