Please be aware about MCap, the meaning inverting the behavior is because each market BTC/BCH has a diffrent volume and MCap, in this way no warrantee of all Alcoins are currently on momentum, but in general if you trade Altcoins its moment to trade VS BTC no VS USDT.
my expectation is about around 6 Months with ups and dowsn but meanwhile the Bitcoin is on Bullish market the behavior be the same till some strong (Super Strong) Correction, around 60% MCap starting with ATH