the king of all coins is Bitcoin. but if you mention the king of all ALTCOINs then I say yes. because bitcoin no one can compete. however Ethereum can still be rivaled by Binance at this time. we can see the current popularity of Bnb which is getting more and more enthusiasts and users of the Binance smart chain. and binance has such a large volume that it has a chance to become the king of all altcoins. 1 level below bitcoin.
BNB is the coin which is supported by Binance, and they always push the coin cause it is their native token. On the other hand, Ethereum has much more real-life uses, many projects are running on Ethereum smart contracts and it is a sleeping giant. The only reason for its popularity is Ethereum blockchain is the oldest and dev are well educated to develop their projects on Ethereum blockchain than other alternative blockchains. As it is older, it is also the most advanced in terms of security and reliability. Although the fees are much higher here but you know, people give more priority to security than fees. I think Ethereum is much stronger and more durable than BNB.