Bitcoin's appreciation is directly proportional to alt coins. However many people hold altcoins for two reasons; In fact, people use cryptocurrencies for two specific reasons:
1. To hodl as a store of value for long term gains.
2. As a tradable asset, to increase one's investment portfolio.
More so, we have seen in many cases where Bitcoin does a bullrun and leaves altcoins behind. Usually, in this instance, the alt coins begin to show a red indicator - reduction in value, this is because of the gap between them. In the mean time the altcoins will play catch-up.
So generally, BTC is like the base pair for all altcoins. But as the market continues to mature we would see many more pairs like in the traditional capital/Forex market. But for now depending on what exchange you are trading on, you could have ***/BTC, ***/ETH, ***/USDT, ***/USD, and ***/BNB.
Noted on this Sir! Based on your explanation as an investor as of the moment it is much better to have greater portion of BTC in my portfolio and the remaining should be the altcoins. Altcoins is much better investment if the market continue to mature still better get those coins.