"So who IS the One? Some of the evidence points to Sinclair, but
other bits seem to indicate Delenn. Yet neither seems to fit all the
facts above."

Exactly.

What you have here in your message are two pieces of the puzzle.
You're confounded by the fact that somehow they don't quite seem to fit
into one another. That's because there's one last piece missing in this
part of the picture, which fits in between them. The intent is to put
this piece into clear view in year three, probably between episodes 8 and
11 approximately. At that point, the question of the One will be fully
answered.

jms