During the next days after the last halving the Alts market cap more than doubled and BItcoin's dominance dropped quite a bit. It will be interesting to see what happens this year though it seems that the interaction has changed with altcoins and Bitcoin been more correlated perhaps due to the larger FIAT pools with stable coins. In 2016 most altcoins had to be adquired via Bitcoin (ETH/BTC, XRP/BTC, LTC/BTC, etc) and this year this is not the case anymore since there are many altcoins paired with stablecoins.