One thing for sure, if bitcoins goes down, the altcoins take a hit also,often times it is worse for altcoins. The bitcoins dominance has been indicative of the in last couple of months,never gone below 60 per cent
It is as simple as that, bitcoin is simply too big and if it goes down in a strong way then almost all altcoins will follow this movement as they cannot resist the influence of bitcoin, and since they are smaller for the most part they are hit even harder as people prefer to either get bitcoin to reduce their losses or to get fiat and stay away from the market until things get a little bit better, this is why it is important to never hold altcoins for the long term or you risk suffering tremendous losses in a short amount of time.