ΛCDM as a Phenomenological Ceiling: Where COCM Enters as a Structural Alternative

ΛCDM remains the benchmark cosmological framework because it is parsimonious and phenomenologically powerful, but its success does not constitute physical closure. The Concentric Orbital Cosmological Model (COCM) is proposed as a structurally motivated alternative, entering at the precise point where eective ingredients in ΛCDM stand in for closed dynamical mechanisms. This paper develops the comparison at three levels. Empirically, persistent tensions the Hubble tension, the cusp-core problem, and the missing-satellites problem raise the question of whether the standard framework is resolving those features or parametrically accommodating them. Structurally, dark matter and dark energy remain unclosed components at the microphysical level. Epistemologically, ΛCDM is parsimonious in parameters but not necessarily in explanation: it summarises unresolved physics eciently without deriving why the t takes the form it does. The second harmonic predicted by COCM for non-zero orbital eccentricity is presented as a signature of non-circular dynamics, not an ornamental correction. Its relation to cusp-core phenomenology is discussed as a structural analogy, explicitly not as a derived solution. The modied closure of the Poisson equation in COCM is treated as a conditional consequence of the harmonic modulation, distinct from the standard treatment in kind rather than degree. All claims carry explicit epistemic labels. The primary prediction ωz = 11.1991, registered on 14 May 2026 (DOI: 10.5281/zenodo.20178768), is unaected by these arguments. The decisive observational test is DESI DR3.