Any sort of verification presumes that you have an initial trusted checksum against which to verify, so I don't believe this solves the separate problem of obta

Any sort of verification presumes that you have an initial trusted checksum against which to verify, so I don't believe this solves the separate problem of obtaining such a checksum. IIUC your question here boils down to "what is the point of a hash tree?" as opposed to e.g. a list of individual chunk hashes. The answer is that a hash tree lets you verify an individual chunk by looking at the hashes of O(log(N)) chunks rather than having to look at the hash of every chunk.