Maybe a dumb question, but do people looking at alt coins compare them to USD? I mean you can't directly cash out into USD (except maybe ETH and a couple of others?)...so basically you're always at the mercy the way BTC is moving. USD is more stable and you can get a true sense of how the alt coin is moving, but is that essentially irrelevant?
So in general do people only look at the alt coin to BTC? It puts another layer of challenge with how volatile BTC can be at times.
only the popular altcoins which will be listed on certain exchanges will be traded against both bitcoin and USD. these exchanges are those top exchanges that have BTC/USD pair.
and about the price, when these altcoins are traded with bot bitcoin and USD there will be a connected (one way) between bitcoin price and their price which will in turn go down if bitcoin goes up and vice versa.
but other should not be affected by bitcoin price since there is no USD relations but what happens is that they are affected because people will stop trading these coins and the demand drops so price goes down.