In a bull market they tend to rise more than bitcoin: hence in a bull market the bitcoin dominance tends to lower.
Conversely in a bear market those coins tend to drop faster than bitcoin: the bitcoin dominance tends to rise.
it is not only about the speed of rise/drop. it is about the fact that there is only
1 bitcoin which is going against
1700 altcoins. that is why calling it "dominance" is wrong to begin with. if altcoins were good then the real dominance of bitcoin should have been 0.05% instead of forty something! being at forty... just proves that altcoins are indeed shitcoins.
Whay that? most altcoins can be traded only versus bitcoin: when market rises avi people tends to sell Bitcoin (larger market cap) to buy smaller cyptos that can be lifted more with less capital influx.
The everse happens ib a bear market where investors, actually scalpers, revert to bitcoin as a safe haven in crypto land, to protect their investment (they cannot sell for fiat in a single trade).
the altcoins have other markets including USD and other fiat, other altcoins like ETH, LTC, Doge,... and even stable coins like USDT. the problem is people want to use their bitcoins because they want profit on their bitcoin not on their fiat or altcoin,... which is why they trade altcoins versus bitcoin mostly.