There is a difference between an altcoin index achieving greater dominance than Bitcoin because it affects the lack of risk in the cryptocurrency market and the lack of profit for altcoin compared to Bitcoin, and an altcoin/bitcoin pair rising, which may happen without affecting Bitcoin's dominance.
In general, since the risks are high, everyone will prefer to invest in Bitcoin, especially since there is no strong competition from altcoin, so the Bitcoin dominance index will remain high.