Bitshares price performs like most alt-coins (anything non BTC). In a bull market they exceed BTC - in a bear market they underperform. I see nothing as of yet to cause concern about bts vs. other alt-coins.
But if you hold bitUSD, or even better, bitSilver/ bitGold, then you will be mostly unaffected by crypto market dropping. We've got a bit farther to go to make that situation a reality - but it's so close I can taste it.