Basically the creation of altcoins includes eth to compete with other coins including btc, but eth crying is indeed the best btc competitor, because now there are many new crypto projects that use eth's platform, and that is one factor why eth can be called the best altcoin.
Yes, the ETH platform is one of the factors that make ETH so good, but competing with BTC, I dont think so. The both coins are just in the market, going its own way.