Altcoins follow the trend for bitcoin, many of them are worthless and will only gain some value only when the market is in an excessive bull. Many of the top coins are not deriving value from use cases, only from occasional pumps and dumps
What you have been saying is not true and some altcoins can still able to get a huge pump even without the help that must have come from the bitcoin. I do agree with if it's not all of top coins are getting their price from the use case but it's coming from the speculation.