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.
However, sometimes there are times when the price of bitcoin is stable, the price of the altcoin will go up considerably. it's just that at this time it is not visible. however, the potential for a high price increase could occur at any time this time. even though the price of bitcoin is more dominant, there will definitely be times when the altcoin price will go up by itself. well, I also hope it will happen at the end of this year, or early 2021.