Leaving aside the contentious issue of environmental costs being hashed out in the cmments, here's one more reason to be long ETH rather than BTC: there is no other cryptocurrency ecosystem that can even remotely compete with all the developer activity taking place in ETH.
You know how crypto enthusiasts are always talking about all the different possible applications of blockchain technology, including DeFi, smart contracts, decentralized file storage, decentralized communications, decentralized social media, and even decentralized management of natural resources? Well, most of that stuff is being built on ETH. Which means that going long ETH is a kind of indirect way to go long a lot of those other future blockchain applications and technologies. There's just so much happening in the ETH space, and basically nothing happening in BTC.