Here's my longest running account with no funding changes from December 2013 to today:
http://seaofbtc.com/harrisonkinsley/honeybadger/client/1 It will take a while to load. That's done by automated day trading, and it's done using a mindless grid-strategy that anyone could do by hand, it's not high frequency. I just choose to automate it so I don't have to sit there all day and don't miss any trades. Bitcoin is volatile, so it works, and I've significantly beat the market, but there are plenty of totally possible events that could leave me far behind market performance never to recover again.
It's hard to know if your profits are a result of alpha or beta. Measured in BTC you are clearly ahead, but then you've probably been at least partly in USD a lot of the time. The market has been in a more or less continuous decline, so you would have archived about the same result by just staying 50/50 in BTC/USD. Unless the bitcoin price goes back up and you're still ahead you can't really know if your model beats the market in general or just the current market conditions.
No doubt the decline has helped us to beat the market since we're not fully invested, but there have been multiple occasions when price has been in the positive gain, or the fund is at +20% while market is still in the negatives. The main account started while price was $700 per, and breaks even right now at $500 per BTC, while market is still - 27%.
So sure, the decline has helped us beat the market, but the actual profit is gained from volatility, and we'd be beating the market with this much volatility in either direction.