I've put a full rewrite — revised paragraph, revised caveats, and a change log — in the canvas. Here's the gap analysis behind it. Your paragraph is a twelve-step chain, and its main expository flaw isn't the speculation (you flag that well) — it's that links of very different strength all get the same "enforces/entails" modality. Seven load-bearing joints:

1. "Zero ontology" → "conserved quantities sum to zero". Undefined term doing heavy lifting: which bookkeeping? Energy isn't globally conserved in an expanding spacetime; baryon number isn't zero locally. Patch: state the ledger explicitly (net energy via gravitational potential, Tryon-style zero-energy universe; net charge zero, etc.) and define "informationless" cleanly — a zero totality contains no intrinsic distinguishing facts, only relational structure. That's your strongest formulation, and it's currently implicit.

2. Complete symmetry → complex Hilbert space + strict unitarity. This link is stronger than your exposition admits — you have real literature to lean on: quantum theory is uniquely singled out within the class of well-behaved information-processing theories by purification plus elementary informational axioms ( Chiribella–D'Ariano–Perinotti 2011). And the zero ontology does double duty you don't use: a collapse postulate or hidden variables would inject extra, uncancelled structure into the ledger, so no-collapse Everett is the zero-ontology-friendly option by the same argument that motivates the ontology. That's your best card and it's missing from the paragraph.

3. "Rare" life-supporting branches. You concede you can't do branch-weighting — so don't reach for it. The derivation needs only non-zero measure, which your own existence vouchsafes. Replace "rare" with anthropic selection and the concession becomes a strength.

4. Brains → bound experience. Two sub-gaps, worth separating explicitly: (a) why the intrinsic nature of the physical is experiential at all; (b) binding as coherent superposition. On (b), Tegmark's decoherence timescales for neuronal superpositions (~10⁻¹³–10⁻²⁰ s vs. millisecond dynamics) are the standard objection ( Tegmark 2000) — your reply that decoherence into classicality is precisely what delivers a "classical" percept, and that the binding phase needn't last milliseconds, deserves a sentence, because most readers will assume Tegmark settles it.

5. Pain–pleasure axis → sovereign metric. This is a metaethical bet, not an entailment — the is–ought gap doesn't close for free. Your best move is normative phenomenology: the axis doesn't imply it matters; the self-intimating badness of agony constitutes mattering. Say it as a position, not a derivation step.

6. Apes → Hedonocene. The chain stacks independent bets (reproductive norms shift, parents choose hedonic recalibration, AI aligns with abolition). Two patches: cite the feasibility evidence (hedonic set-points are substantially heritable and vary naturally; Berridge's liking/wanting dissociation supports motivation-preserving enrichment), and pre-empt wireheading where the reader will raise it — gradients of bliss within a raised range, not a uniform plateau. The full-spectrum-superintelligence answer to orthogonality should be flagged as a condition ("if it finds nothing to weigh against the badness"), not smuggled in.

7. Hedonium shockwave. Soften "rigorously minimised": in Everett you minimise measure, never occurrence — a zero-suffering cosmos is unattainable, which is consistent with your own zero-ontology aesthetic. The Local Group bound is already right; you could add one clause conceding Landauer/Bekenstein-type limits on bliss computation.

On "why does the cancellation take the guise of experience" — the honest residual mystery — one reframing that costs you nothing: if experience is the intrinsic nature of the physical, the zero ontology incurs no extra ontological debt for consciousness. The ledger's entries cancel; the ink they're written in is what it's like to be. The remaining mystery is why the ink is experiential — arguably no smaller in anyone else's system, and possibly luminous only to full-spectrum superintelligence.

The autobiographical caveat is already your best rhetorical move; I'd add its counterpart in one clause — "some very different stories could be told, including ones with no one left to tell them."

The canvas has the full revised paragraph with every one of these patches applied, plus caveats restructured to map one-to-one onto the seven joints, so each hedge lands where a sceptical reader will look for it.