I also invested in ethereum, because eth has proven to be a good altcoin and ETH has also proven to be able to survive under bitcoin in recent years and until now ETH is the best altcoin. Of course I don't know much about it, but I keep hearing discussions about how accelerated ETH's development has been to date. Despite high gas fees, ETH remains the number two investment choice after bitcoin.
The point is that what makes me confident and want to invest in both is because Eth and Bitcoin are two blockchain technologies that are very popular and of course very widely used today. This proves that both are assets that have great potential in the future and as an investor it is mandatory to own both.
Have you check despite that Bitcoin does have high transaction fees, a lot of people still use it and never complain about it is the same way ethereum community like Ethereum despite the high transaction fees. Bitcoin is even better because sometimes it's cheaper except the days when the mempool is full but ethereum on the other hand can remain like that for as long as the network is busy and people still spend money on the fees and like it, they have strong community foundation.
Solana was the closest alternative to ethereum but I guess the hype around Solana kill it before it time, they made a lot of partnership that didn't favour them and is the reason why they are where they are today. They were even lucky they made it back to almost 3/4 of the previous all time high and the meme trend else they wouldn't come close to sit where ethereum is today in the top 10 market cap. Though, regardless of the market sentiment, it will be difficult for any altcoin to replace ethereum.