Do not trade Alts with BTC these days, You will just lose
I do not recommend to trade alts with btc these days otherwise you will be just loosing your money. As BTC hitting its ATH, the prices of alts are dumping even if it is BNB or any other coin whichever was stable in the last months. Just trade BTC/USD only.
Your suggestion is good but it works only when BTC is either Bullish or Bearish and BTC Dominance Index is higher ( more than 70%) but When BTC is stable and BTC Dominance Index is around 60% then it is good opportunity to entry in alts (Top 20 on coinmarektcap except XRP) and sometimes traders book huge profit during alts Rally. During the rally alts also show good performance not only against stable coins but also against BTC
https://cryptoguidepro.com/bitcoin-btc-dominance-index-meaning/