The term "Bitcoin dominance" is made possible participants in the market have enabled it. When the market gets hit, people sell their alts in exchange for Bitcoin. This further increases the dominance of BTC as people see it to be more stable than most others coins out there.
The same BTC dominance you feel is ruining the market is what alts feed on. When Bitcoin increases in price or enjoys a price surge like it did in 2017, altcoins benefit alongside. This is why most alts attained their ATHs 2017, it wasn't necessarily because of their fantastic, but because the market is very liquid and BTC was the driving force. Heck, even shitcoins were mooning too