You mean, using server-sent events for things that are not events but data, one row at a time?

Of course that'd be slow, but that's equivalent to sending one websocket frame for each row, or one file per row over HTTP multipart. Hardly talks to the speed of either protocol.

I disagree. SSE makes one design easier. If that's great, great. If not, not. But per-unit SSE is ships more slowly because it doesn't allow for easy batching.