There is no doubt we are going to have an altcoin season just like from 2017 event. I believe before BTC hits its maximum ATH for this season altcoins will start to blast headed by high market cap altcoins headed by ETH, XRP, LTC
I do not remember any altcoin had good rally in 2017. By 2018 January/February ETH had big rally up to 0.1 BTC.
This 2021 must be a typical bull rally in my opinion; I am seeing both altcoins and bitcoin get into bull run at the same time. ETH and LTC may continue to have big values but I doubt what XRP is going to do as it was delisted on most exchanges but now they are cleared from SEC's issue still there will be less chances for it to test a new ATH this year in terms of BTC value.