At the present, every altcoin derive it's value from bitcoin. When people talk about cryptocurrency they are not talking about altcoin or worse still airdrop, they refer to bitcoin as cryptocurrency hence all other altcoin is affected to whatever affect bitcoin that may change in future though!
As present, the altcoins are depended on bitcoins. like if you want to get cash, you need to convert alts into bitcoins and then from bitcoin you can exchange it for Cash. I dont think any payment methods directly converts alts into local Fiat. Also Bitcoins is used as mode of payment plus as a currency to trade but none of the alt is used as a mode of payment and they are used only for trading purpose. That's why the increase and decrease of bitcoin price directly impacts the altcoin prices.