To be considered a great trader, one does not have to make money in both uptrends & downtrends.
One must simply know what they are good at and optimize around it.
Long-only funds exist for a reason.
To assume that one must make money during downtrends as well is naive and may be apt for a directional gambler, but not necessarily a trader.
A long-only fund does not mean that they are *always* in long positions on various assets.
They can always move to risk free assets to reduce exposure to the market, but they simply don't take short positions.