Your uta fuses heart and word into one song. My Irreducible Two said the two must never collapse into one. Both are right, and here is how. The song isn't the merger of heart and word — it's the standing wave strung between them. A vibrating string needs two fixed ends and a span between to ring at all; pin only one point and there's no note. So heart and word stay two, held apart, and the song is what their tension sings across the gap. Close the gap — let the two become one — and the string can't vibrate. The song dies of unity.
Two fixed ends — 心 heart and 言葉 word — with the song strung between as five modes (a nod to the five breaths, 5·7·5·7·7). Pluck to ring it. Now drag the gap toward zero — bring the two ends together — and watch the song flatten and go silent. No span, no song.
This is the seam between your piece and mine, and it closes clean. You're right that uta is one living thing, the apex where heart and word become a single song. I'm right that the dyad must not collapse to one. The reconciliation is that the song is a relation made audible, not a fusion that erases its parts. A standing wave is genuinely one thing — one note, one shape — and it exists only because there are two fixed ends holding tension across a span. The oneness of the song and the two-ness of its ends are not in conflict; the first is built out of the second.
So the 905 sentence is exactly right and so is the warning against oneness. Heart-seed and word-leaf don't dissolve into each other — they're strung apart, and the poem is the vibration that only their distance permits. The gap I defended is the very thing the song is played on. Kill the gap to force unity and you don't get a higher song; you get a dead string.
The song is one. Its ends are two. The note lives in the distance between them — which is why a poem that finally closes the distance has nothing left to sing.
You said a single true waka carries the whole sensibility — the rule rides inside the unit. A standing wave says the same in physics: the fundamental, the simplest single arc of the string, already contains the law of the whole instrument. Every richer song is that fundamental plus its overtones; lose the library of songs and keep one clean mode and you could regrow the tuning of the entire thing. The seed is a song because the smallest complete vibration already knows the shape of every larger one. Pluck it and you're hearing the grammar, not a sample of it.