And naturally, altcoins benefit only when BTC is up, but when BTC is in buying phase, most alts die;)
That's because of Bitcoin dominance it will always have an impact as long as Bitcoin dominance is that higher maybe when Bitcoin dominance is lower than 30% then the price of some of the altcoins will not be pegged in Bitcoin anymore but on dollar, but it will take years before that happen.
Anyway, Bitcoin is the leader of the cryptocurrency market in all respects and its dominance in the market is almost irresistible. Even the closest competitor, Ethereum, lags far behind. Nevertheless, Bitcoin and Ethereum are more in demand for investors than other altcoins. There is no need to have high hopes for altcoin anytime soon.