I feared new altcoins will be left out so i start selling some coins for bitcoin because it can be a big blow if altcoin fails to surge like in 2017 after bitcoin reach a new ATH, what do you think? And what would you have done in my position
It varies from project to project, yes what you did was the right though if you aren't holding at least the top 10 coins in CMC. Nowadays many altcoins are just replicas of others with nothing new to make them relevant. Also, for someone who want to hold long term most altcoins aren't worth it because swap etc. Furthermore, anytime any day, holding BTC is the best bet as it stands to give more returns unlike other altcoins. While a greater number of altcoins aren't worth it and will surely miss out should there ever be a surge like that of 2017, altcoins like Eth won't be left out. So like I earlier stated, it depends on the type of altcoins.