It doesn't have to be that bad. Users are likely to have more bandwidth available than is needed to stream the file (if they didn't, then the streaming will never work).
Unlike simple HTTP streaming, the clients can use this spare bandwidth to download some blocks from the end of the file, even when streaming from near the start. So a sensible torrent streamer can still ensure that later blocks are not too rare.
The increase in seeds from a more ergonomic protocol offsets the downside. Especially if the population has mostly the early blocks, but most of the population wants the early blocks, then there's room for much leech/leech sharing
Unlike simple HTTP streaming, the clients can use this spare bandwidth to download some blocks from the end of the file, even when streaming from near the start. So a sensible torrent streamer can still ensure that later blocks are not too rare.