A Common European Transition, Unevenly Received: Cross-Country Heterogeneity in SME Resource-Efficiency Convergence, and a Baseline for the CSRD Omnibus Reform

A companion study documented that the resource efficiency adoption gap between medium-sized and microenterprises narrowed by over 80% across the EU27 between 2017 and 2024, but its EU-aggregate design could not establish whether this was a Europe-wide transition or a few national trajectories, nor which mechanism drove it. This article decomposes that finding into 27 country-specific convergence parameters using a two-step estimation and meta-analysis strategy, and tests whether the 2021–2022 energy price shock, renewable energy endowment, or environmental policy stringency explain the cross-country heterogeneity. Heterogeneity is robust to estimator choice (I2 = 53.1%, p < 0.001), ranging from intense compression in Romania, Austria, Germany, and Spain to null or reversed dynamics in Estonia, Slovenia, and Slovakia, and is driven disproportionately by the largest national SME populations. The average convergence effect is more fragile, excluding unity under a conventional interval (random-effects IRR 0.905, 95% CI 0.820–0.999) but not under the more conservative Hartung–Knapp–Sidik–Jonkman correction appropriate for k = 27 (95% CI 0.818–1.001); we treat it as indicative rather than confirmed. None of the theory-driven moderators explains the heterogeneity (all coefficients below |0.029| SD, all p > 0.57), a null substantiated by a formal power analysis and, for an internal initial-gap moderator, by a split-sample design removing a regression-to-the-mean artefact present in a naive test; this rejects national-policy-mediated coercive pressure specifically, not supranational or network-transmitted channels. Two exploratory, purely descriptive extensions accompany the analysis: a small non-EU contrast group shows convergence not visibly different from the EU27, though underpowered to adjudicate between mechanisms; and services-sector SME share shows a nominally significant, non-multiple-testing-robust, association with stronger convergence. Published as the EU’s Omnibus I reform narrows CSRD-obligated reporters and caps value-chain information requests to smaller partners, this country-level baseline provides the reference point for assessing the durability of SME sustainability convergence as new data become available, with direct implications for EU-level SME greening policy.