Altcoins prices right now are dependent on bitcoin. Everything usually goes down when bitcoin goes down.
If we were to scrutinize their price charts, everything that you've just said was true. One factor that attributed to this fact i think, is that every major exchange offers BTC trading pairs (where you can trade BTC for alts rather than alts for fiat or USDT). Because BTC is the top coin being traded for other alts in terms of market cap, volume, and general popularity, it is thus at the center of the crypto economy.
Nevertheless, the fact remains that Bitcoin and Ethereum [or any altcoins] differ in purpose. Essentially, Bitcoin is a digital currency and Ethereum is a decentralized network of applications. Although in a way, Ethereum developers and companies depend on the Bitcoin network for its stability and security.