both work and have their own role in the development of the crypto market.
not everyone is capable and friendly with the bitcoin market. the best alternatives are altcoins like ethereum.
but thinking of the two of them as rivals is indeed very far away. I would probably prefer to pair Cardano, Polkadot, and Binance as rivals to ethereum.
Bitcoin is way ahead of those alts and with high popularity of Bitcoin there's no rivalry but another alternative which trying to succeed from this industry. And with those named alts you mentioned that's better competitions in terms of ETH, they more likely to share trying to be the next successful alts inside this market.
ETH and BTC are not coins that can be compared, they are clearly different from each other and they also have their own goals, both ETH and BTC are good coins for investment because they are the king and queen of all crypto assets.
Good coins for long-term investment, solid project that keeps on gaining appreciations of the market.
If you like to have passive investment, these two coins have that capabilities. Make sure you to have that nerve to keep your asset on hold while the market continue to move.