The coming new phase for BTC

Litecoin is the first fork of Bitcoin, Bitcoin Cash is also a fork of Bitcoin; so is Dogecoin, Bitcoin SV, etc. Yet except for Bitcoin, all the other coins have long pivoted into a long-term downtrend even though they belong to the same Bitcoin family. Are they fundamentally different from Bitcoin? maybe a little, but not that different. Is the first-mover crypto the only true cryptocurrency there is? or does it include second-class cryptos like Ethereum who underperforms Bitcoin long-term but still manages to maintain long-term relevance? or will they all slowly start their downward pivot into irrelevance like the omens of Litecoin and Dogecoin suggests? Let me know your thesis and reasoning behind it. Thx.