Any blockchain can end up with high fees and slow confirmation times if network load grows at a fast pace. ETH was once cheap and fast to use, as not many people were using it. Things are quite different now that ETH reached mainstream adoption. Gas fees are extremely high, while transactions take hours to confirm on the Blockchain. This could happen with BSC in the future if it continues to grow in popularity. That's why it's important for developers to focus on scaling the Blockchain in order to keep fees as low as possible.

Regarding the question to which coin is better, I'd say ETH is better than BSC simply because it's decentralized. Of course, ETH is ridiculously expensive and slow to use. But that's nothing if you care most about decentralization, security, and reliability. BSC may be cheaper and faster to use than Ethereum, but it's utterly centralized (largely controlled by Binance itself). Projects have to either sacrifice decentralization to obtain scalability or vice versa. For different needs will be the type of cryptocurrency to use in real life. I think both ETH and BSC will survive for a very long time because of their strong communities backing them every step of the way. Just my thoughts