You can compute max drawdown, Sharpe and Sortino for a crypto-asset exactly as for a stock. The arithmetic works. The comparison is what breaks, for three reasons that have nothing to do with opinion.
1. The history is too short to contain a cycle
Our own equity backtests cover roughly five years and we say plainly that this window does not include the 2008 financial crisis - a caveat printed on every strategy page. Crypto's usable history is shorter still and contains no comparable episode of a credit system seizing up. A statistic computed over a period that excludes the thing you are worried about tells you very little about that thing.
2. The drawdowns are of a different order
Equity strategies we publish show simulated worst stretches in the range of roughly -27% to -64%, and we print the worst ones rather than hide them. Major crypto-assets have repeatedly fallen further than that and stayed down for years. A Sharpe ratio summarises an average; it does not warn you about the shape of the tail.
3. The clock is different
Crypto trades continuously; equities do not. Annualising a daily standard deviation assumes a trading calendar, and the two calendars are not the same - so the same formula applied to both produces numbers that look alike and are not.
What this means for a rules-based approach
A backtest is only as honest as the window it ran on - the whole argument of how to read a backtest. Where the window cannot contain a full cycle, a track record cannot carry the weight people want to put on it. That is one of the reasons we publish no crypto strategy.
Educational material - not investment advice.