When BTC bull runs again, I expect BTC to run first and then the alts to lag and eventually if BTC does well, it eventually flows back into the alts.
The reason they were crashing in-tandem this year and rallying in-tandem was mainly because it was a bear market. If BTC tanks, then people know the alt will tank, they dump their alt into BTC, dump BTC too. But usually in a crash, the alts would always get hit worse, because money was flowing out the alts first, and then into BTC, and then into USD.
If BTC begins to run in a real bull market, most alts wont run that well just like in 2017... until BTC runs enough that the market favors re-balancing into the alts, in which case alts would do great. There's not panic in a bull market, and the bull market can't run unless BTC runs... so it has to hit BTC first. Even in this latest BTC move, a lot of the alts have not kept pace.