Of course if not all, majority of altcoins is paired with bitcoin. So obviously, bitcoin is the measuring stick of all crypto coins. People really don't understand that altcoin market is more volatile than bitcoin, and they think that they can make quick and big money in altcoin, yes it's true, there is this pump-and-dump method in altcoin. But if you are not that careful, chances are you are going to lose your money very fast as well. And just observed that we are near all time high, or as others have said, we have reach in already. But look at the top 10 altcoins, most of the are not even close to 50% of their previous all time highs.
Since 2019, more exchanges create more USDT pairs for altcoins and traders have more convenience with more pairs to trade altcoins. It does not change the role of bitcoin in the market, as a leader, as a King and its effects on altcoins and capital flow are unchanged.
Altcoins are pumped and dumped with news from upgrades, development process, partnership and with general trend of the market. Trend is a friend and can help to get profit with altcoin investment. I would prefect to invest in silent altcoins rather than those altcoins have rallied too much this year.
I believe there is no definite pattern here. There were also countless of times when the price of Bitcoin is going down and the prices of altcoins, at least the leading ones, are soaring high. Case in point, when Bitcoin reached around $20,000 mid December of 2017, the price of Ethereum was only around $600. By mid January of the following year, Bitcoin has already lost around 30% of its price but Ethereum has more than doubled.
It is the capital flow and capital cycle. Whales manipulate the market but their ultimate goals is collecting profits. They get profit in Bitcoin, cash out to USD or stablecoin and dump altcoins at same time. They come back to manipulate altcoins in BTC pairs, get more BTC, and manipulate BTC again to get more USD or stable coins.
Of course, Bitcoin is the key player. It always has been and will always be the key player. It is always the dominant coin in the market but you cannot create a fixed formula which says when Bitcoin goes up altcoins go up and when Bitcoin goes down altcoins go down as well.
Altcoins are more vulnerable with news and law regulations than bitcoin.