Why does my strategy underperform buy-and-hold?

Usually because 2021–2026-style bull markets are nearly unbeatable by anything that ever sits in cash. Every day out of the market is a day of forfeited drift, and most timing rules are out of the market a lot. That doesn't automatically make the strategy bad — check what you bought with the underperformance: shallower maximum drawdown, smoother equity curve, less time exposed. If the strategy lags on return AND matches buy-and-hold's drawdown, it's genuinely adding nothing — discard it. If it cut the worst loss from 35% to 18% while giving up a few CAGR points, it's doing exactly what timing rules honestly do. The comparison to run is always same asset, same window, risk and return together.